I am looking forward to the day it supports table access methods that enables variety of use cases out of box.
Something like rocksdb as PG backend would be fantastic. Yugabyte does this but it's not PG.
OrioleDB seems interesting, not sure it's what you're after but worth a look.
Salesforce runs Salesforce on postgres with LSM:
https://vldb.org/cidrdb/2026/a-multi-tenant-relational-oltp-...