Considering the license is the same as PostgreSQL, I assume there is a real possibility the OrioleDB Engine to be upstreamed into Postgres itself?

Right now OrioleDB is an extension, which comes with PostgreSQL core patch. The mid-term goal for OrioleDB is to become a pure extension. The long-term goal is to make OrioleDB part of PostgreSQL core.

Is this similar to MySQL's InnoDB? (which is also MVCC and does not require vacuum)

Great to see innovation on PostgreSQL storage engine layer!