[throwaway92394]

But more importantly - can we embed ID3v2 inside ID3v2?

[blep_]

You can encode the inner one into a QR code and use that as album art. The rest is just optimization.

[lawik]

I haven't tried but that should work fine unless the specific parser gets up to some shenanigans.

[pwdisswordfish0]

Sure, every frame announces its own length in the frame header, so the frame content iself does not need to be escaped (apart from the usual escaping of MP3 synchronisation markers, called „unsynchronisation“, but that’s not relevant to the question at hand).