I'm speaking generally, but I'd say 3E/3.5E influence with some 2nd Ed. and 4E bits here and there.
I'm going to guess that song by first... hmm... 6 notes
"at-will"
Did I win?
Okay, what I really think could happen:
From 2d: Classes being more unique and distinguished one from another, perhaps with more interesting leveling curves; better armor and weapons are there as a long-term goal, instead of just starting game in full-plate; perhaps more class-based narrative features (Paladin Handbook).
From 3d: Probably a large amount of skills and feats.
From 4th: Equal contribution of all clases to combat; per-something abilities; 5 minutes rest; getting rid of memorisation (obvious).