Not only are there glyphs for talented abilities, but there are glyphs giving severe disadvantages in an area of the game. Take these three glyphs for example:

Glyph of Moonfire - Increases the periodic damage of your Moonfire ability by 75%, but initial damage is decreased by 90%.
Glyph of Mindflay - Increases the range of your Mind Flay spell by 5 yards but it no longer reduces the target's movement speed.
Glyph of Avenger's Shield - Your Avenger's Shield hits -2 fewer targets but for 100% more damage.

The moonfire glyph is very good for pve, but gives you a severe disadvantage in pvp. The mindflay glyph may be very useful in some pve boss fights, useless in others, and crippling for yourself for pvp. The avenger's shield glyph is good for boss fights, but a disadvantage for aoe tanking. With glyphs like these you can actually be worse at a specific part of the game compared to someone who doesn't have any glyphs at all.

Sure you would, that is practically two of the same thing. Any sort of glyph that increases survivability would help in both cases to some degree.

Because currently, talents have such a huge effect on a character that it's simply not viable to perform a role against your talent spec unless it's trivial content anyway. So blizzard is giving free talent spec switching. On the other hand, glyphs sound like like an interesting extension of the talent system but compared to the changes based on your talent tree the benefits of the glyphs are rather small, and you could easily perform a role without the best possible glyphs in most cases.

And then as far as glyphs, if the cost is high enough it forces players to make decisions about what role they want to be optimized for. I don't see this as a flip-flop from any previous stance. It's not like you can change race between pvp and pve, even if for example orc warriors are better at pvp than tauren warriors, but tauren is better for pve tanking. I think blizzard saw how trivial the talent respec cost was at 50g, and rather than increase it and upset a lot of players they are going to just make the glyph system the more or less permanent character customization system.

I could be totally wrong, but I think it's just as likely of a possibility as free multiple glyph specs.

Then obviously if you are a druid who likes the option to spam moonfire in pvp, you should not take the moonfire glyph. I like the way glyphs have both advantages and drawbacks, hopefully players have to carefully consider which glyphs they take instead of mindlessly taking the 4 best raiding glyphs and then switching to the 4 best pvp glyphs twice every week.

The problem with glyphs is the same than chainpotting or stacking flasks and elixirs. Blizzard needs to balance encounters around the fact that many people will use everything to enhance their chances on killing the boss, so the boss has to be tuned accordingly often making it mandatory for "casual" raids to do it, too if they want to stand a chance at beating the encounter in a "reasonable" time, and yes, some glyphs have a big impact. The changes to flasks and pots clearly indicate that they want to make a sort of baseline that can be expected of everyone and is not too expensive and restrict everything that goes beyond.
Therefor I wouldn't expect expensive reglyphing and me personally I would hate it, because even with my paladin alt I switch roles in kara/ZA/Heroics sometimes three times or more per evening just because someone else comes online and wants to join the group and I just don't like being suboptimal in any of my roles just because glyphs are to expensive. Of course i could do the heroic without optimal glyphs but it's way more fun to be the best you possibly could be.

Either it is really cheap or free or totally restricted and I don't think it will be restricted because it contradicts the respecc for free/take part of every part of the game thing and, as I said before, some glyphs would NEVER be used if you can't swap them (like aforementioned Mind Flay or Avanger's Shield Glyph)

/EDIT: typo, probably still some more there ^^

But they DO re-tune encounters regularly.

Remember how impressed everybody was with the first guild on their server to clear Kara? Remember the pre-nerf Magtheridon before they simplified cube-clicking?

I'll never forget the sight of a shadow priest tanking Ragnaros shortly before the BC release.

Bosses are incredibly tough at release, making it possible for only the best of the best hardcore min/max guilds to succeed.

A series of nerfs and the introduction of easy "welfare" gear makes it possible for hardcore, midcore and "casual" guilds to have their turn. Many of these guilds maximize their consumables, and many do not. But eventually everybody has their turn.

Blizzard tunes encounters so that you can only be FIRST if you have time, skill and a fortune in consumables.

You CANNOT make people do that. You're making people who play more aspects of the game suffer more because they're enjoying more parts of the game. If you want to be competitive in PvP you must get the PvP glyphs, otherwise you're at an inherent disadvantage in an area where the difference between winning and losing is a single crit over more than a hundred thousand damage done. If you want to push the limits in PvE, then you must use the best possible raid glyphs, or you're at an inherent disadvantage.

You're trying to penalize the people who enjoy more of the game, which is the exact opposite of what you should be doing, either by making them put even more time in to fund their endeavours, or by limiting their capabilities. People who are interested in more aspects of the game should be rewarded.

You have it backwards too. Noone should ever get a bonus for specializing except for their own personal skill. You should never limit what people can and cannot do in a game artificially like that.

I think it's a bit crazy to say they would NEVER be used. Especially in this community, where most people will do everything they can to maximize their performance. That also implies there are no or very few players that focus only on PVE/Raid content, and don't care about the drawbacks.

It's only a drawback if you want everything to be free/no consequences/no specialization. I'm surprised how many people posting are opposed to having options for specialization, is homogeneity that desirable to everyone?

There's a reason the arena realms have everyone in the same gear with the ability to choose any race/class, and I'll give you a hint, it's not homogeneity.

I agree to an extent, that blizzard will balance encounters based around everything available.

I simply disagree with your conclusion, which is that hardcore raiders will respec glyphs to raid.

Maybe blizzard intends that the hardcore raiders glyph for raiding and suffer slightly in pvp as a result. Maybe blizzard doesn't want you to be the best at healing AND the best at tanking AND the best at DPS all on the same character just by throwing money into respec costs. Perhaps blizzard's intention is that raiders sacrifice a little bit of pvp capability in order to take the best possible raiding glyphs.

I mean, that is what WoW is all about. You have DPS classes that sacrifice the ability to tank or heal in order to put out a little bit more DPS than the hybrids. You don't see mages crying about the inability to spec into healing or tanking do you? It's all part of the deal, you give up capabilities in some roles to be better at the one you prefer.

If you really want to be able to fill 3 roles optimally, you can always level three characters.

I think you're missing the point that people are trying to get at. It's not necessarily that they want to fill 3 roles fully optimally at the expense of other classes. It's that if glyphs are swappable people WILL swap them to be as optimal as they can be for their class and spec.

Even if a Prot paladin, or a Warrior, or a Resto druid is "sub-optimal" for a given encounter, if he can become "more optimal" through the use of glyphs he will do so.

I was targeting that more towards the idea that everyone can be everything at once with minimal effort. There's no difference between one druid and another because they don't have any decisions to make.

Why shouldn't you limit what people can and cannot do? Why is it artificial? Technically even having classes makes everything 'artificial'. It's a game, there are supposed to be restrictions/limitations/choices. That's where the fun is at, in a PVE game.

Not if the cost is high enough and the benefit small enough.

See BOP jewelcrafting gems, see enchanting ring enchants.

If glyphs are cheap and easy to change, yes I'll agree with you. However that remains a big unknown at this point.