Combos cannot and should not be consolidated in PvE. What you're talking about would change the PvE combat system entirely. I don't play a lot of jobs, but every single one I do weaves (sometimes double weaves) ogcds/instant abilities between the weaponskills required for their combos. And if even one job is impacted negatively, then the whole concept crashes and burns.

There is already a limit to the maximum number of skills the devs can implement and give us access to during PvE, and I am sure they are well aware of it. This is reduced greatly due to the game having players that use a controller. This basically gives the devs a maximum of 48 skills (excluding passive traits) to give players access to during combat, or 3 cross bars. The pet classes are an exception and use a 4th, and actually have room for additional skills on this bar if the devs wanted to go there.

There are simpler ways to reduce/prevent button bloat if this is your chief concern. For starters, some jobs have innate gcd skills that go unused because there is always a better gcd to use. Think Repose for WHM. I also believe the role skill system is either being revamped, or (hopefully) being done away with entirely. There are a lot of skills here that can just go away and we won't miss them. Several other skills were wrongfully taken away from their respective jobs, and you can probably expect jobs like AST and WHM to lose access to skills like Eye4Eye come 5.0.