Psionics needs to be at least partly integrated into the core rules of 4th Edition, IMHO. It gets neglected or dismissed by many just because it's non-core and thus seen as being less balanced, less well-designed, and less appropriate for D&D. Since it's been included in each edition as little more than an afterthought as a late expansion or small section of the 1E DMG, psionics has remained only haphazard in its quality and usefulness, warranting many of these opinions.
But 4th Edition really should include some psionic rules and background material; at least 1-2 base classes, 2-3 prestige classes (or whatever may replace them in 4E), and a modest selection of powers. I'd also like to see it have some barebones support for other things, like Oriental Adventures (i.e. a ninja variant rogue, a samurai variant fighter, a wu jen variant wizard, a shugenja variant cleric, etc., just simple notes on appropriate modifications).
Of course, ideally, I'd like to see the core 4E books each have a few sidebars (or small section in the back) describing how some of the material fits exactly into the official settings (whether or not they're all still supported). I.E. a blurb about how arcane casters/divine casters/psionicists could or do fit into Krynn, Athas, Oerth, Faerun, Kara-Tur, Zakhara, Maztica, Mystara, Planescape, Spelljammer, etc.