That would be the ideal solution. Though I'm not certain it's possible while retaining the "D&D feel".
I quite like the 4e style too - and I'm not sure it lacks the "D&D feel", at least for me.I rather like 4e's approach to the issue, with implements that are as big a part of casters' arsenal as weapons are for warriors. I like the Harry Potter / Gandalf style wands and staves that actually help characters do magic.
Gygax in his DMG seems to imply that in AD&D casters will want wands and staves if they are to be effective in combat, because of the risks of casting spells in combat. In practice I didn't really see it work out like that, but there is still the kernel of an approach there that is different from the 4e one but makes wands and staves as important to casters as weapons and armour are to fighters.
I'm not particular worried about the magic items not being incorporated into math assumptions. 1e functioned just fine that way and I don't see why 5e wouldn't. Magic items should provide bonuses for the PC whether in hitting, doing damage, or having additional special abilities, not be required to keep up with Monster Jones next door.
They need to have some baselines for advice. So they can say "in the average game PCs will gain this much magic and you can account for that by doing Y". So things stay balanced. Which also helps for organized play, where they can say that "this campaign is Average Magic, so at level 10 you need to make X adjustments and at level 20 you need to do Y" to their campaign staff.
It's also very helpful for new DMs who might need a little advice on what is expected and what impact it has on the game.
Maybe I'm misunderstanding, but the first of the three posts I've quoted seems at odds with the second two. And it's not clear to me which approach WotC is taking.In terms of the system expecting or not expecting items, what I'm hoping for are tweaks to the encounter building guidelines so that you can add or remove XP from the budget based upon what the party has. Based on this article, I'd love to be thinking in a few months: "Hmm, well, the party just got two extra magic items last time which bumps them into the high magic column at the moment, so I need to add X to the encounter budget. Oh, nice, that means I can add a Gargoyle and still keep the challenge about right"
If the GM is expected to adjust encounter difficulty based on magic items wielded by the PCs, then in effect items are part of the maths -but incorporated via the encounter building tools, so on the GM rather than the player side. I don't see anything wrong with that, but it seems worth noting it for what it is. In fact I prefer it to the approach suggested by billd91, for this reason: if GMs aren't expected to make encounters mechanically more challenging in response to PCs acquiring items then the practical consequence of acquiring items is that encounters become easier. And easier encounters are, on the whole, less interesting. So the reward for acquiring items becomes one of the game becoming less engaging - which is actually the Monty Haul problem that Gygax warns about in the quote from his DMG.
EDIT: Because D&Dnext seems to prioritise "the adventure" over "the encounter" then you could incorporate items on the GM side by changing the "adventure budget" rather than the "encounter budget" - ie the more items you have, the more you have to do between rests if you are going to succeed at an adventure, whatever exactly it is that success consists in. This is still taking items into account in the maths of the game.