I think one thing a lot of people are discounting is those on the "I don't want it dumbed down side" are looking at it as simply 111 or 222 but what about simply allowing us to trigger combos with same or even varied button inputs just less overall buttons?
An example I'll use is Devil May Cry. Now, ignoring all the more advanced things, at it's most basic level you have Punch (P) Kick (K) and Shoot (S) or in XIV 1 2 3. On their own those buttons do exactly what you'd expect but it's when you combine them that you get combos, PKP dose one thing, KKP dose something else PPKKS will do something else.

So what if XIV tried something like that? To use DRG as an example rather than reducing it's combos to 11111 and 22222 you instead gave them 3 new buttons True thrust (T) Impulse Drive (I) and Jump (J) for example.
Now, pressing T,T,I,J,T is your Full thrust combo while I,J,T,T,J is now your Chaos thrust combo (Fang and Wheeling included of course)

With this, 6 buttons just became 3, however you're still using varied inputs and needing to think about what you're using and when just not needing to take up as much space on your hot-bars.
This could also allow for new moves to be added without actually adding a new button.