I don’t have a dog in this fight other than interest in ML-family langs generally and Haskell as a pervasive interest everywhere I go outside of Haskell. But...
No not really, if your language is intentionally designed to be a foundation for other languages. So many lisps are trivially host languages for other languages at their core. Even JS is at this point, with the widespread use of Babel and various bundlers. Those languages themselves are seldom very different underneath that.
Making a "language laboratory" for typed languages, (as opposed FFI with lowest common denominators like C or so-and-so untyped, garbage-collected language) is an open problem. I think it can be solved, but until it is, it's wishful thinking to pretend a multitude of similar languages doesn't result in tragic fragmentation of a small community.
TypeScript seems to be doing alright? Maybe there’s something I’m missing but TS is basically a type checker on top of everything JS compiles to, including the whole Babel universe and compiler transforms that support macros and arbitrary AST manipulation. Even its standard config offers a multitude of similar languages.
Having a type language on top of an untyped one is fine (except for perf). It's having multiple typed ones that compose well and aren't just reskins of the same basic type theory that's the harder part.
No not really, if your language is intentionally designed to be a foundation for other languages. So many lisps are trivially host languages for other languages at their core. Even JS is at this point, with the widespread use of Babel and various bundlers. Those languages themselves are seldom very different underneath that.