Remathilis
Legend
I'm not sure how to respond to this other than to say that 4E actually did do that; they just didn't openly announce it.
A lot of concepts introduced in late 3rd Edition books were 4th Edition concepts. Take a look at the knight from PHB2 and see if you notice some of the similarities to the 4E fighter and the 4E warlord.
The late 3.5 stuff bore only passing resemblances. To whit; a lot of ideas from the Player's Options line (attacks of opportunity, Universal School of Magic, customizable PCs) made it into 3e, but to say that PO was a preview of 3e would be very misleading. Sure, there were lots of hints as to things, but there was no "Play 4e Today" moment. That was intentional. 4e was breaking the mold and you couldn't graph any area of it onto 3.5 and have it work. You couldn't drop healing surges into the game the way 4e used them without radical changes to cure magic, resting, healing potions, and the like. The changes were far greater than "giving clerics spontaneous casting". Thinks like the knight, or reserve feats, or Book of 9 Swords, hinted at the direction of 4e, but to say "You can get a feel for what a 4e game might be like by using a warblade instead of a fighter in your next session" is highly disingenuous. Whereas, I did get feel for 3e using 2e and some bolted on concepts like spontaneous cures, sneak attack dice, and upwards AC. It wasn't perfect, but it got closer than 4e did in its run-up; which left me in the dark on how the game would play until the PDFs leaked.