I only skimmed it, but don't like it due to few reasons.
1. Both BIP and details on GitHub have zero references.
2. They chose SPHINCS+ which have 49,856 bytes. Without also proposing to increase block size, it would massively reduce TPS (transaction per second).
I recall Bitcoin Foundation had major internal and external issue many years ago and i almost never hear about them afterwards.
Personally, I think this BIP is better than what is proposed previously regarding "post-quantum in Bitcoin".
Do you mind telling us what makes you think this BIP better than other proposal/BIP?