Re: Would PostgreSQL 16 native transparent data encryption support database level encryption?

That's not quite right.  A PostgreSQL cluster (in the traditional sense, which means one PostgreSQL server handling a particular endpoint) is isolated from any other clusters on the same machine.  

And, to be somewhat blunt, is Rubrik prepared to pay for it?  This engineering effort needs to be funded by someone, since engineers have to eat.  This is not to say that any feature someone is willing to pay for will make it into PostgreSQL, but an effort of this size, to have any hope of reaching the point of being accepted, will need someone to pay the salaries of the people working on it.