This is how it works in PvP, and it's awesome. It doesn't break your combo and typically builds your resource or refreshes your buffs. The overall DPS is lacking still, so melee and tank still want to get onto the enemy to perform. Of course, it has to be competitive because FL and RW kind of has a lot of situations where everyone kind of assumes a ranged DPS role, though I think a lot of the general game feel principles can still apply.

IMO this should be done for PvE. It should at least add time to your buffs and not break your combos. It just makes the combat feel more engaging if you are encouraged to interact with the enemy more frequently with effective APM. In addition, in general I feel like if we are going to give the player a button, it should feel awesome and more useful. Some fights melee/tanks will basically have 100% uptime sans transitions so it won't matter, but for those where you need to disengage, that option will seem a lot more attractive than losing a GCD or two across the fight.