I plan to use Orleans to handle a lot of the heavy HA/scale lifting. It can likely stand in for Redis in a lot of cache use cases(in some non-obvious ways), and am anticipating writing a Postgres stream provider for it when the time comes.. Will likely end up writing a Postres job queue as well so will definitely check out River for inspiration.
A lot of postgres drivers, including the .Net defacto Npgsql, support logical decode these days which unlocks a ton of exciting use cases and patterns via log processing.