Luke Dashjr opened a discussion regarding why Bech32 was omitted from previous P2SH2 improvements.
For those unfamiliar with the concept, the idea is to have the address include the single SHA256 hash of the public key or script, rather than RIPEMD160(SHA256(pubkey)) or SHA256(SHA256(script)). The sender would then perform the second hash to produce the output. Doing this would in the future enable relaying the “middle-hash” as a way to prove the final hash is in fact a hash itself, thereby proving it is not embedded data spam.
Bech32 seems like a huge missed opportunity to add this, since everyone will probably be upgrading to it at some point.