What are some use cases (if any) that the language is not suitable for?

Probably kernel code, or cases where allocation randomization is important. Seems like with goose you may end up executing more deterministically (but still it can randomize where these N data stacks start), but because it's single threaded workers (in essence), all data construction would follow the same pattern, hence an attacker (something snooping your memory) would know easier where things would be.