While I'm sure happy to know that all errata and clarifications plus the (few) universally acknowledged needed corrections will be printed in the revised corebooks, I am very skeptic about the consequences.
I really doubt that the new books will have only clear rules, and will be errata-free, let's be ready for this. We'll never get error-free books
Plus, and most importantly, although many players (and some authors as well) dislike something from the core rules, be it a class, a spell or whatever, there are also many players that are perfectly fine with them. Change the Ranger and you may have more satisfied people than before, but you'll have new rants from the ones who like him as it is now.
Sure: first check the differences, and if you prefer the un-revised rules, simply don't buy the new books; but they will become the new standard, and this messageboard will see more arguing than before... which isn't necessarily a bad thing, since we like it a lot
I think that if Monks, Bards, Rangers and maybe someone else is "heavily" fixed, basically it'll paved the road to a habit of simply write your own class and make it as you like. The DMG's Witch is anyway a suggestion to this, isn't it? Fine. I don't see any problem with it, except exactly the difficulties in balancing the PC with the others. I wonder if they are playtesting all the new classes or if they are just trusting that if so many of us think the Bard needs a fix, then it must be true. But there will still be thousands of house-ruled fixes for the Bard even after the revisions anyway...
Neverthless, if some of our expectations written in this thread become real in the new books, they'll make a great improvement in our games.
Personally, I'd like to find at least:
PHB:
- better explanations of some under-explained abilities (Wild Shape, Rebuke/Control Undead...)
- better explanations of some skills
- extra feats from splatbooks that are suitable for non-fighing classes
- full stats for few Animal Companions, Familiars, Divine Mounts AND comprehensive lists (similar to the spells lists would be fine)
- a longer list of Summoned monsters/nature's allies
- more Bardic Music forms (I supposed that the ones in PHB were only examples, but I've yet to see other ones printed anywhere)
- better book binding! definitely better glue
DMG:
- how to calculate EL and how to really use it, or otherwise wipe it away forever
- a decent section on traps
- a decent section on area spells
MM:
- comprehensive pages on how to write a totally new monster from scratch
- ECL for all playable creatures
- ultimate rules for advancing creatures
- favored class for every monster that takes level
- touch and flat-footed ACs in the stats
- at least a couple of sentences about every creature's reason to exist in your world
- one picture for EVERY missing monster (the worst thing when I bought MM was to find out I would have never seen the Balor, my favourite monster)
But I'm quite convinced that of the MM 100-pages increase 99 pages will be because every monster will basically get his own page (they are over 500 - like the back cover says - only if you count each Dragon's age as a different monster: count 10 Dragons instead of 120, don't give single pages to Animals and Vermins and you fit them all in 320 pages).
A final word:
I hope that game mechanics will be almost untouched, or they may have unpleasant consequences on a lot of material already published.
I also hope that core classes won't change heavily. I have my own ideas on how I'd fix some things I really don't like from Bard, Wizard, Sorcerer, Paladin, Monk, Druid and Ranger, but I have resisted until now to change them, and they all still worked fine in my games; nobody prevents a DM to change whatever he wants, but although many of us wish for a new Ranger or Bard, I'm sure that each has its own new version in mind, and few will be much more happy with the ones they'll find in the reviewed PHB if they are very different from the current.
). Frankly, I would *not* want a come back the old AD&D2 look. Easley covers... *shudder* 
