persistent_term to replace ETS for caching

Hi guys,

At work, we cache about 5.3 million entries in ETS. The system works
perfectly, no issue so far (many years).

During a brainstorming session, a colleague suggested to switch to
persistent_term instead to avoid ETS term copying.

Pretty simple: we check if the Key exists in persistent_term. If yes, we
are done. If not, we get it from ETS, move it to persistent_term and send
it back to the caller.

Question: is there any limitation(s) on persistent_term usage? Stated
otherwise, can we create 5.3 million persistent_term <K,V>?

Any suggestion/idea/thought is very welcome.

/Frank