In an interview on Gothamist, John Linnell talks about the plans for the next in the series that started with "Here Come the ABCs", and will soon be joined by "Here Come the 123s".

What are you talking about? We’ve sort of cooked up a rough idea for the Disney DVD that will follow this one and at this point we’re thinking it will just generally be about science for kids. Besides that, we’re in the middle of being home and writing regular They Might Be Giants rock songs but there isn’t a particular schedule for another grown-up record yet.

(Found Via Spare the Rock)