An interesting pet project for someone to attempt would be a language with fully-specified arithmetic.
So rather than declaring vaguely that you want an "integer", you'd specify bounds, signed-ness (two or one's complement), and what happens on overflowing the bounds (wrap / saturate / exception / trap / set flag / set NAN etc.)
Saturated arithmetic intrinsics are widely available but generally not used by generated code. Similarly I've never seen an attempt at doing "integer NaN", which could be quite useful in some situations.
You'd probably also want some flags to say "give me a compiler error or warning if this code doesn't compile to intrinsics and is being emulated instead".
So rather than declaring vaguely that you want an "integer", you'd specify bounds, signed-ness (two or one's complement), and what happens on overflowing the bounds (wrap / saturate / exception / trap / set flag / set NAN etc.)
Saturated arithmetic intrinsics are widely available but generally not used by generated code. Similarly I've never seen an attempt at doing "integer NaN", which could be quite useful in some situations.
You'd probably also want some flags to say "give me a compiler error or warning if this code doesn't compile to intrinsics and is being emulated instead".