I have never heard of this, i wonder if its a bug or its intended. I cant imagine that its intended
Druids have been able to pounce and ravage out of shadowmeld for quite some time. all this does is even the playing field. That, and make the flippy jump the second most important benefit to being a night elf rogue.
The change can't be older than 4 months: Cataclysm Subtlety Compendium. Druids were already able to use it at that time, so I guess it either was intentional or they're both bugged now. However as druids still seem to be able to do it after such a long time, I'd go with the first option. That or Blizzard doesn't care enough (though maybe they will now that Rogues have discovered it, who knows).
I just did some further testing, it seems that every ability that works in stealth also does in Shadowmeld: Ambush, Garrote, Cheap Shot, Sap, Pick Pocket, Recuperate, SnD, Vendetta, CoS, Distract, Sprint. They latter ones except the first three also don't break it, just like normal stealth. Wasn't able to test Disarm Trap.
And some napkin math shows me that a Shadowmeld->Garrote would be around 455 DPS for me (according to my last Baleroc logs), for an average of 9 energy each 2 minutes. I'm not sure how much DPS the 9 energy would net if spent on Mutilate or other abilities, so I cannot tell the actual DPS gain I'm afraid.
Also it does reset the swing timer.
I believe druids gained this ability when shadowmeld (and warstomp) were changed to allow functionality in animal forms. Historically, they have had to be moonkin or tree to activate their "on use" racials, I believe the idea from Blizzard having been that you don't gain an active racial if you are some other kind of species or creature type entirely.
In any event, the addition of two new druid races presumably caused them to rethink this, and now druids can freely use racials regardless of form. Even though druids (and rogues) do not get stealth bars, cats have been able to macro or directly cast openers, and now rogues can too.
Of pve interest:
Assassination: Garrote (mentioned before) gains you a bleed proccing venomous wounds. It seems obvious that this is a dps increase, but do note it resets the swing timer.
Combat: I do not believe this is a dps gain for combat. I have not done math, but a garrote's damage, assuming a couple ticks crit (with bleed debuff) is going to be about that of a crit SS for 6 energy more- but combined with the swing timer resetting, I doubt this will be of great benefit.
Subtlety: An extra 10 seconds of expose weakness from Ambush every 2 minutes should see this spec gaining a decent amount. Edit: Premed should be macroed in here too.
Cheap Shot can be used an additional time when faced with stunnable mobs. This extra utility could be important during Ragnaros transitions, but Cheap Shot is not normally a clutch pve ability.
Garrote has a 3s (major glyph up to 4.5s) silence attached, and sometimes this could be useful if a mob is silenceable but not stunnable.
Also of PvP note:
Sap can be used more reliably and quickly in a CC chain, as shadowmeld does not always drop combat and allow reentry into stealth promptly- now it can be done very quickly to an opponent who has dropped combat (from a fear, blind, etc.).
As listed above, a macro can be made for each move, of the style:
You can also call up a second bar with your moves on them, but I doubt that would be a popular solution.
A multifunction macro of this sort can also be created:
/cast Shadowmeld /cast Premeditation
/cast [nomod] Cheap Shot; [mod:alt] Ambush; [mod:ctrl] Garrote; [mod:Shift] Sap
Note that these macroes all require two button presses as a minimum- the first press activates shadowmeld (no global) and the very next one casts the opener (edit: or does both premed and the opener).
Note that I have contacted the author of Dominos (Tuller) regarding this issue, and he responded that it seems a reasonable time now to implement support for Shadowmeld action bar paging (i.e. the same bar as for Stealth).
So chances are good that it'll be supported soon.
It's also rather easy to mod this yourself, simply add a line addState('class', 'shadowmeld', '[stealth]', GetSpellInfo(58984)) to barStates.lua under the class == "ROGUE" section (around line 112). You then can select Shadowmeld as a valid option additionally to Stealth for bar paging.
Of course this doesn't work correctly for other races than Night Elfes or other classes (I've heard that Warriors can use Charge out of Shadowmeld?), so it's only a temporary fix.