wahoo!!!
You have perfect timing with this video as i am just now looking into adopting Nimzo-Indian for Black, and Catalan is a big deterrent with all the White repertoire books on it-- Wojo Weapons, Avrukh, Strategic by Donaldson, etc.

I will definitely watch this in more detail and try to leave some kind of clever comment later. But for now i will have the honor of leaving the first (non-clever) comment.

White can avoid this line by delaying c4, right? I don't play the white side of the Catalan, but I recently picked up Play The Catalan from the library in order to get a few ideas for black.

1. d4 Nf6 2. Nf3 e6 3. g3 d5 4. Bg2

And black should probably transpose to a system with Be7 or c5. What are your thoughts on this?

Against c4 but with Bg2 instead of Nf3, I think black can play 4...a6, and white has nothing better than 5.Nf3 (Berkes-Aronian, 2002, e.g.), after which you play 5...dxc4.

If he plays 5.Qc2, there is an interesting idea of Novikov's, which is to play 5...Nc6, and 6.Nf3 Nb4 7.Qb3 dxc4 8.Qxc4 b5 9.Qb3 Bb7 worked out well for black imo in Larionov-Novikov, 2004. 5.c5 b6 is nothing. So I'd recommend just playing a6 in that move order.

Delaying c4 is trickier.... let me look some more.

So one idea when they never play c4 is to play b5!? So 4...b5!? is one possibility, as played by Leko, Kramnik, Adams, etc.

Maybe I'll do a 5th video where I talk about move order tricks and neo-catalan (nf3/c4 move orders, etc.) That might be a long video, though.