libaco VS typedlua

Coroutines, async/await and general multicore support in the type system. Most languages by now either have some variant of async / await (JavaScript, Kotlin, Swift, Rust) or super-lightweight threads (Go, Elixir, Java via Project Loom), or they just have Monads which supersede coroutines entirely (Haskell, Scala). It's at the point where some say a language isn't suitable for production if it doesn't have good multicore support (also see Rust speeding through getting async/await even though they already have Send + Sync). Even Python and C++ have coroutines now, and of course there is a coroutine library for C which uses macros and low-level magic.

it's based off MIR, does it have something to do with https://mlir.llvm.org/ ?

for typed lua, there is another effort https://github.com/teal-language/tl in addition to the mentioned typescript approach: https://github.com/andremm/typedlua

Gradual typing. This is what TypeScript is: you have some typed values and untyped values, and want to verify and possibly optimize the typed code while permitting the untyped code to compile. Besides JavaScript/TypeScript, you'll find gradual typing on pretty much any other popular untyped language including Python, Lua, and Racket. Mojo is also going to have gradual typing.