The actual storage engine is written as an extension - these patches are mostly to improve the TAM API. If these are accepted by the community then it should be simpler for anyone to write their own Storage extensions.
I think (correctly) it will take a lot longer to upstream the extension - the PG community should take a “default no” attitude with big changes like this. Over time we will prove its worthiness (hopefully beyond just supabase - it would be good to collaborate with other Postgres providers)