I feel like this option works for PvP because of the fact that PvP is basically a super simplified version of PvE against other players. Personally, I can see combo buttons as maybe a very specific macro for very specific classes, like BRD when you can use Pitch Perfect/Refulgent arrow, that could change to whatever situational skill you need, but otherwise does not account for a majority of decision making. Since this thread is specifically about WAR, I'll use it as an example. It has 1 starter, 2 mid combo extenders, and 3 finishers. So, to be able to use any finisher when you want to, you would still need 3 slots on an action bar. So really, would it help anything? Probably not.
That is however, just my opinion, and opinions are as varied and as different as the people who hold them. Perhaps it would help some people to make the class more usable, but I'm with Galgarion on this, part of an MMO is managing your hotbars and keybinds, and knowing your job well/knowing what you need to do at all times. That is, after all, the spirit of an MMO player who ends up progressing in Extreme/Savage/Ultimate(Abbrev. E/S/U) content versus someone who can't get past Extreme content.
TL;DR: I don't care if they're in the game, but I personally see no need for them.