Gentlemen, may I make a modest suggestion? Rather than approaching this
questions as if you were the only people on earth, why don't you start
by examining other database systems with external user defined
procedures? This would not constrain your choices but might shorten
both the discussion and trial and error phases.

Netfrastructure, as you are aware, supports only Java procedures. It
has a custom JVM to support dynamic class loading for development and a
non-blocking garbage collector, but these are not essential. What is
essential is rigorous security and consistent transactional semantics.

Although the Falcon code that interacts with the JVM is open, the JVM
itself is not yet open source. But, if anyone has any questions has to
how Netfrastructure resolved the questions you are now considering,
please ask and I will do my best to explain.