The reason I have been against the idea so far is that an integer type is easily accomplished using the FFI and user code. Here is one example (not quite what you're asking for, but hopefully instructive): https://github.com/darinmorrison/purescript-int64
As long as it is efficient and compiler supported (I.e an int add ends up as the proper instruction, and improper assignment ends up as a meaningful compiler error) I think the implementation doesn't matter. Going to
Natural numbers and such feels like a separate topic from just having efficient and type safe (modulo overflow) integers.