I'm pretty certain it's not going to break action bar mods. What it seems to break is making keypresses perform actions without pressing an actual action button; in other words, a mod could create a valid set of action bars using the 120 buttons provided for this purpose by Blizzard, but won't be able to make a button press do different things dependant on who/what you're mousing over. That'd mostly break click-casting mods though, as well as the Necrosis style mods and possibly autobar mods, I'd suspect there's a work-around possible to make something like Decursive work again, but it'd require a lot of re-coding on the part of other mods.

As for the skill required in manually decursing. It's about as skillful a job as doing 'conveyor belt' work. Especially in some of the worst examples in MC.

I'm more worried about the thing mentioned by Gibybo. Though Target's Target and Raid frames should still work; I'm more wondering how it affects things like raid#target or targettargettarget.

I'm rerolling rogue.
Then I can talk shit about playing with skill too.

I'll stab you ingame exog.

There's no reason to remove click-casting (like clique). I'd be hugely disappointed if they broke that functionality.

If blizzard breaks fastcast they have to allow spell queuing.

Without that i dont think ill bother playing.

I'm holding out hope between this change and the introduction of Mass Dispel, Blizzard is affirming it wont be introducing new dispel clickfests in The Burning Crusade. I'm still quite leery though, considering there's no Mass Remove Curse nor Mass Abolish Poison.

To give you an example of what a healer feels like on a raid...

Get a priest friend, or watch a friend do the benediction quest. Hit the "V" key. Watch, click, heal/dispel the health bars. Scream as they overlap. Curse as you try to pinpoint the 3 or so npcs that need dispelled. That's about what it is.

Current mods don't pick your target and automatically heal them, it's basically just streamlined information. Allows you to know what's going on in your raid without having to sort through a mixed jumble everytime.

Ever the optimist, I'm hoping they change this. Emergency monitor is not a giant deal, decursive will suck but whatever. Some mods are just irreplacable and will make the game far less enjoyable, without implementing any skill value into it.

Do we know if this applies to macros along with ui mods?

One of my favorite enhancements to my WoW experience is a macro I wrote which backstabs and then turns combat on if it's off after the backstab (i.e., it turns on autoattack if the backstab fails due to position or lack of energy).

Not game breaking, but annoying if I won't be able to do it anymore.

Not trying to be all elitist here, but I guess going with the minimalist approach to mods and addon's may turn out to be an advantage for me. Even with decursing I started doing it manually in AQ. Like previously stated, however, I would be disappointed by more 'chromaggus' style fights where mass decursing is the road to victory. That mechanic is rediculous, not to mention boring. My hope is that with the lowered raid size Blizzard is trying to take some of the more mundane aspects of the game out. Sitting in one spot and spamming the same button until you either A. Run out of mana, or, B. win, would be a huge disappointment.

One would hope they include a built-in alternative to fastcast...
Doing patchwerk for some healers is simply not possible given time constraints if they have poor pings.
The decursing crap is interesting and all... and I dont think decursing Noth will be neither fun nor skillful, just a pain in the ass.
Most of what they're removing here seems to be mods oriented around making menial tasks simpler - but I suppose its to remove all the automation you can encode. Versatility of mods was one of the best things about them imo... almost felt like certain encounters assumed you were using them.

You have 40 healthbars up on your screen during raids and watch each one for any kind of debuffs which you automatically attempt to dispel?

I guess I'm not the norm, but this is what I do too. I used decursive for my first couple of Lucifron kills way way back, but then decided it was basically cheating and that I didn't need it anyway. The only raid mod I've ever used is CT raid, and that only to see everyone's health, debuffs and MT targets.

Having 40 health bars and their debuffs up the whole time doesn't make me responsible for the whole raid though, we still do assignments but this way if something goes wrong I can still see everyone's status. It allows me to do everything I need to do.

Basically, I've just never been convinced I actually needed any mods to help me heal. :)