Eh? The LuaJIT and K interpreters definitely fit into L1 instruction cache. (And have since well before 2013 probably.) Honestly I would be kind of surprised if most interpreters for reasonably small languages don't fit into icache. Sure Python's not going to any time soon, but most interpreters are really not very large.

You could get Windows NT 4 running in a processor cache these days.

Forth interpreters probably fit into L1 on modern processors.

I'm guessing u/hinkley meant having an API for the cache, so a compiler could generate instructions to prefetch cache lines (and maybe even keep them hot) rather than depend on automatic (heuristic) cache management.