I mean it would certainly be nice for people who may get flustered having so many skills but at the same time, why not? No reason to use your 2-3 combo without the one, letting them be simplified into 1 button (didnt watch the pvp info, wasnt interested) but letting it swap to the next skill with the same press. Does remind me a tad of Tera (i think?) where pressing Space would cast the next recommended move?

Would also save more space too, id imagine for some classes it may be a bit harder to pull off like Monk where your combos could go any direction but those with limited combo branches I can see the benefit.