Estlor
Explorer
I think there is a reasonably large amount of compatibility between the two; in fact, a look at Malhavoc Press's Iron Heroes and WotC's Tome of Battle and you see the roots of 4E already being tried out in 3.X. The biggest difference isn't healing surges or "lack" of Vancian magic (aside: Vancian magic didn't go away, it expanded to every class). The biggest difference is the tactical aspect of 4E. A lot of the spells available to 3.X would break the assumptions made by 4E.
If you were going to do a 3E/4E hybrid, you'd almost need to adopt the base assumption of either 3E combat or 4E combat and go from there. Honestly, if you took 4E whole cloth, diversified the rituals and created more that could be cast "on the fly" as it were, and gave wizards/invokers/druids more utility powers, you'd have the 3E/4E hybrid without any significant work.
In other words, 4E's apple didn't fall as far from the D&D tree as some of its detractors would have you believe. Honestly, after playing 4E's classes, I never want to go back to 3.X's.
If you were going to do a 3E/4E hybrid, you'd almost need to adopt the base assumption of either 3E combat or 4E combat and go from there. Honestly, if you took 4E whole cloth, diversified the rituals and created more that could be cast "on the fly" as it were, and gave wizards/invokers/druids more utility powers, you'd have the 3E/4E hybrid without any significant work.
In other words, 4E's apple didn't fall as far from the D&D tree as some of its detractors would have you believe. Honestly, after playing 4E's classes, I never want to go back to 3.X's.