It appears that in Burning Crusade, Blizzard will be disabling all "click-to-cast" functionality in UI mods. (UI mods can no longer cast spells of their own accord during combat, even with a mouse click or button press.)
This effectively means that RDX's ability to cast spells on units from RDX windows will be severely curtailed or completely removed in the expansion. This will also effectively eliminate other click-to-cast or autocast mods like Decursive, Clique, et cetera.
I'm afraid I can't post a reference link, since Burning Crusade is still in closed alpha testing. The information comes from an anonymous source who I am sure is under an NDA.
Personally I am 100% confident that this is true; obviously it's up to you to make your own judgment on whether you believe it at the moment.
Cannot change key or mousebindings while in combat. This is done to prevent work arounds like
-You could just rebind the spell to the mouseclick before cast and rebind it to the window action after. This may require a double click instead of a single, but would probably still allow the casting of spells by clicking.
So, what this change means is that mods cannot be used to cast spells, meaning that stabbing buttons for decursing and buffing is no longer allowed. Point and click healing functionality is still fine, obviously. I'm not paticularly bothered about this change myself, provided they don't create any more lucifron/chromaggus/noth style encounters, or if they do, mass dispel will be fine.
It seems TargetUnit() is also blocked, and TargetByName() no longer exists, but /target works - guess they revamped the targetting commands too?
Of course, this has the added side effect of making old encounters much more challenging post expansion.