Creators of Erlang have a Lisp background, and one feature of the Erlang VM (BEAM) that I'd like back-ported into Common Lisp is their process.
An Erlang "process" is cheap to create, cheap to destroy, cheap when blocked, and upon exit performs bulk gc of its allocated memory; e.g., munmap().
Handling tens of thousands of requests per second per node isn't uncommon, and these often have *several* workers per request or connection: hundreds of thousands of processes. Under such scenarios, anything less than this approach to lightweight processes might suffer from stalls during long gc runs that would be avoided or significantly reduced under Erlang's model.
How might we get equivalent cheap ephemeral processes into a contemporary Common Lisp implementation?
In short, you need to write from scratch a new CL implementation. Current ones are not designed with the Erlang constraints in mind.