I loved 3.x
I just couldn't stand creating another high-level NPC caster that lived for seconds but took hours to build.
I guess my point is that there is a lot of things that you can do to "cater" to people playing Pathfinder (d20).
And if one of those things were "backwards compatibility", I would absolutely had shut up, since if Paizo had gone ahead and made a "Pathfinder 1.5" all the power to them. It wouldn't be something I personally would have looked into, but congrats to everyone up for another decade of "d20 catering".
But since that's not the case, I'm here to speak my two cents. And that is to hope against hope Paizo will tap into the probably significant market share that's ready for some lovely player crunch (which d20/PF does splendidly) with classes, feats, subsystems, magic items and so on... just as long as the DM isn't buried in the same amount of crunch, and that the lesson of finally getting rid of LFQW isn't un-learned. (How this is accomplished is not nearly as important than that it is accomplished, and I'm certainly not married to specific 5E implementations)
Have a nice day!
Its sort of where I am heading with my hombrew. Uses the 5E engine and numbers but things like Fort/Ref/Will from 3E, 5E DCs, and it has microfeats. Uses B/X xp though, no archetypes (build your own with feats), and the Fighter is kind of like the Chamion from 5E, tweaked and mixed with elements of 3E and AD&D (scaling saves, feat every second level). Its raw at the moment and only has 5 incomplete classes (aiming for 8).