I'm surprised that people haven't spent more time on Into the Woods in this thread. "I Wish" is the "I Want" song to end all "I Want" songs. The princes have an "I Want" song later in "Agony." Actually, as I review the song list, Act 1 seems to be wall-to-wall "I Want" songs.
I think the idea of needing an "I Want" song in a show is a useful guideline rather than a rule. And while Sondheim certainly subverts it, he does not ignore it. I find it fascinating that George's "I Want" song in Sunday comes well into the show (I consider "Finishing the Hat" to be his "I Want" song). On the other hand, "Now/Soon/Later" begins Night Music, with "Glamorous Life" right after. A wealth of wanting!