I’ve been playing around with it a bit, seems nice. They’ve completely reimplemented Lua and have extended it with a type system and some other improvements. Apparently the interpreter is faster than the standard Lua interpreter and close to the famous LuaJIT interpreter (no JIT mode), and they plan to add a JIT compiler in the future too.
When they talk about not enabling JIT for “client side scripts” they are talking about Roblox, everybody else using it can do what they like.
I watched a talk by one of the devs and they are conscious of not over complicating Lua, which is good. Not all languages need to implement all of the hot new generics shizzle and Lua is popular at least partly because it is simple.