It would indeed be nice for the Mill to solve another old problem (proper tail-calls).
In 2000, there was a discussion about adding tail-calls to gcc.
Would these issues still be a problem on the Mill? IIRC in some contexts there can be a callee-accessible part of the scratchpad provided by the original caller. Would that still be accessible for the new callee? And in the case of portal calls, return appears to revoke all grants. I suspect this behaviour would be inappropriate for tail-calls, wouldn’t it?