Why is there a max size at all?

Looking at ThreadController and your max size. You could've just as easily malloc'd a new block of threads when necessary. Is there any specific reason for not doing this?

Start by reading ThreadController and inspecting how its maximum size is enforced. Check whether dynamically allocating additional thread storage is supported by the Arduino environment. Done would require a maintainer-confirmed rationale or a clearly scoped decision about changing the allocation design.

Written by the indexing model from the issue text.