Regarding recursive functions, would it really be that annoying? We kinda take the ability to recurse for granted, yet it is rarely used in practice, and often when it happens it's unintentional and a source of bugs (due to unforeseen re-entrancy). Intuitively it feels that if `recursive` was a required modifier when declaring intentionally recursive functions, like in Fortran, it wouldn't actually be used all that much. Most functions don't need to call via function pointers, either.

Being explicit about it might also allow for some interesting compiler optimizations across shared library boundaries...