I had an idea about consolidating classes a while back. Now I have a different, maybe better, idea. Why not condense classes? 20 level ones into 10 level ones, 10 level into 5 level, 5 level into 3 level?
I'd probably leave T1-2 as they are, but shorten T3 and below.
BaB, hp, saves, skills and spellcasting would progress normally, but the classes would gain their class features faster, ending with abilities of a 20th level class on 10th level.