I'm surprised no one pointed out that Postgres has *already* been ported
to a new language once. It was originally written in Lisp, and was
rewritten in C sometime in the Berkeley years. (Anyone know exactly
when or by whom? I don't.) You can still see the effects of that
origin in the system's liking for list-based data structures.
But the code base was an order of magnitude smaller and simpler back
then, meaning that a fresh port would be at least an order of magnitude
harder. Like other respondents, I'm not seeing where we'd get benefits
commensurate with the cost.
regards, tom lane