If deciding on whether replacing Pichu...........then YES to Raichu.
If just thinkiing on new pokemon......No Raichu, we need more 'non-overhyped' ones. Also, I only know a few pokemon past the original 150...[always meant to borrow the new GBA games from my friends].....but I think it would be really hard to add new ones.
Pikachu, Jigglypuff, Mewtwo fit fine because they are more 'humanized' than others. Pikachu is never in his pokeball so he absorbs more human culture.
Jigglypuff doesn't have an owner so no pokeball and expresses more human emotions like desire to sing and anger when everyone falls asleep on her. Also, she expresses her anger in a very human way-- by writing on people's faces [I've always wondered how much longer that marker will last, BIC can learn from it].
And Mewtwo is genetically created and can talk {mentally, but still} and goes out and gets himself a home and holds a tournament(movie), what other pokemon would do that?
Following that theory, Meowth is the only other 'humanized' pokemon I can think of, but that specific one is horrible at fighting. But I hope someone can point out a newer pokemon that fits the previous criteria.