But I can speak generally and say: build for modularity and playstyle inclusivity. The founding philosophies of "this is fun... anything else is not" that seem to inform 4e--and are so much as spelled out in the 4e DMG and dragon articles--to me betray an exclusivity in the design and (as put by Irda Ranger
in another thread)
monoculture at WotC's D&D design team.
I couldn't disagree more and I don't understand this stubborn insistence from some that 4e is a limited focus game that attacks other playstyles. It isn't backed up by the system as presented, nor the design philosophy.
4e IS built for modularity and playstyle exclusivity. 3e wasn't. The designers tried to design every little subsystem they thought anyone might want and cram it into the overall game structure. It ended up limiting, rather than expanding game play, as you were stuck with the designers half-baked craft system instead of a well thought out, balanced one (for example). If crafting wasn't a part of your groups playstyle, those rules were a waste or resulted in actual conflict with the system (endless gold loops). If your group was all about the crafting, the rules that were there were not nearly sufficient and you had to houserule them to death anyway.
4e is modular. The core books present the core system and the core component of D&D gameplay - encounter resolution. With a solid, balanced system you can plug away, easily adding whatever subsystems you want. You can take them easily from past editions, other games, whatever, and thanks to tables such as that on pg. 42 DMG, and advice from the section on house ruling its easy to do in a balanced manner.
Want to plug a more involved economic system on the core equipment rules, easy to do. For core gameplay, mundane equipment is largely irrelevant to adventurer wealth. This is, obviously, consistent with every other edition. In 4e though, rather than devote pages to it, and come up with starting gold tables, all PCs get the same and the prices are set a bit artificially because you only do it once. Want more for a low magic game or one where secondary gear (like pitons, chalk, etc) prove very important (such as an exploration/wilderness focused game)? Its easy to institute your own starting gold tables and expand the lists using information from past editions. The gold scale in the game really applies to magic items, so you can even just plug the equipment straight from 3.5 into the game with no problem.
Want crafting or other skill sets outside of the core adventuring set of skills? Easy. Add them in, decide how many of this extra set of skills each class gets to pick. They can do this without affecting their ability as adventurers. Want those choices to affect their abilities as adventurers, add the skills, don't give any from free, just add access to the class lists.
Crafting rules? Use the craft points system from UA or the crappy 3e system if you really want. Use the table on page 42 for the DCs.
The design of 4e lets you add anything your group wants into the game without worrying overmuch about its interaction with the core rules. It also has the added benefit that if your group wants something as part of the game, they are unlikely to look to abuse it, but to use it in the spirit intended. For some optimizers in 3e, all the crafting system or the artificier were good for were endless gold loops.
At no point does the game system tell you how you must play the game. It makes it easier than ever before to tailor the game to your groups playstyle without interference from the rules. The only conceit the game engages in is in saying that the core of gameplay for D&D games is - gaining levels and treasure through defeating monsters and enemies. If this isn't part of your gameplay, then D&D, not just 4th edition, is not for you.
The assumption is that gamers are generally a creative, imaginative bunch. I've never understood the attitude of some in saying - "they took away xxx, my group likes to xxx, now we can't xxx, 4e sucks". Especially as the system is designed to be modular. This will be a major area where 3PPs will find wiggle room, I would imagine - building subsystems (craft, profession/background skills, alternate skill systems, etc.).