replicate per tablespace

Here's an odd question.  Kind of an in the future thing.

I have two db's on two smaller boxes I'd like to combine to one big box.  But one db is replicated and the other
doesn'tneed it. 

I know currently you must replicate the entire cluster.  I was just wondering, would it be a possible way forward to
supportWAL logging per tablespace.  (each tablespace wal's to different directory).  Then, as a logical step, could we
supportreplication per tablespace? 

Just kinda thinking out loud.

-Andy