The system do not need to meet the the wants of the people perfectly, but that still doesn't change that they are incompatible.
If the Pathfinder really wanted things from 4E, they would not have jumped ship and switched to Pathfinder. Likewise, the 4E player would play 3E or Pathfinder if that would fit them better. And while there might be a small portion of people wanting a middle ground between 4E and Pathfinder, many other people would not be impressed by something they abandoned, just with a few concessions added.
Pathfinder players would still play Pathfinder over 4E with a little bit of Pathfinder stuff thrown in.
So thats why WotC can't make a "uniting" edition which is based on previous ones. Instead they have to throw in the wild card and hope for the best.
Except, as a Pathfinder fan, I DO want things from 4E. Not all of them, obviously, or I would play 4E. But off the top of my head:
1. 4E style prep-time compared to 3.5 style prep time
2. self-contained 4E-style stat blocks instead of 3.5 style stat blocks referencing spells in the PHB
3. 4E style XP-budget based encounter building
4. Warlords. Never played one, but I like the idea of them, and would like to see them in Next.
5. Monster Vault style monsters. I DM for my group, and for all the players out there complaining about how all a simple Fighter can do is swing their sword, monsters alternating between the same old claw or bite attacks sure is dull compared to a purple worm that can blast through the ground, swallow a PC whole,
vomit him out for 3d10 + 8 damage and strike at another with his poisonous stinger.
Now, when it comes to the rest of the edition there's things I feel more strongly against that I feel positively for (AEDU for all classes, the necessity of gridded play, Healing Surges, AdjectiveNoun Verbers, etc.), but Next has the potential to handle that as well (i.e. dials you can turn to have healing be as gritty or as gonzo as you like, tactical grid-based rules or Theater of the Mind as default, the possibility for optional AEDU subclasses - pretty much everything except AdjectiveNoun Verbers). It's a game that scratches my simulationist / versimilitude-lover itch while at the same time offering me a system that creaks less under the weight of it's own rules (I'm looking at you, 3.5 / Pathfinder) while giving me the best parts of 4E while letting me optionally exclude the parts of it I find unpalatable.
Now, I know that that is all from the Pathfinder fan's side, so let me ask the 4E players out there: What not-4E features are you looking for in Next? Let's say down the line they balance the classes better and we see some more optional rules that could make Next hew closer to 4E if that's how you'd like to play it. What
else would you do with a modular, turn-the-dials-any-which-way Next?
I mean, yeah, if 4E is your one-system-to-rule-them all, don't switch, you've already got what makes you happy. Pathfinder obviously fulfills that need for a lot of former 3.5ers. But like Jeff Carlsen said, a lot of us are just using the system we have because it's the best of the current options, and I think there are actually quite a lot of us on both sides that'll at least seriously consider switching come release time.