One of the engineers I was working with on a project was from Transitive (the company that made QuickTransit which became Rosetta) found that their JIT based translator could not deliver significant performance increases for A->A outside of pathological cases, and it was very mature technology at the time.

I think it's a hypothetical. The Mill Computing lectures talk about a variant of this, which is sort of equivalent to an install-time specializer for intermediate code which might work, but that has many problems (for one thing, it breaks upgrades and is very, very problematic for VMs being run on different underlying hosts).