> As the typed FP ecosystem is moving towards dependent typing (Agda, Idris, Lean), this becomes an issue, because you don't want the type checker to run indefinitely.

First of all, does ecosystem move to dependent types? I think the practical value of Hindley-Milner is exactly in the fact that there is a nice boundary between types and terms.

Second, why would type checking running indefinitely be a practical problem? If I can't prove a theorem, I can't use it. The program that doesn't typecheck in practical amount of time is in practice identical to non-type-checked program, i.e. no worse than a status quo.