> that's just as hard to compile as one that is defined to trap and end execution on an out-of-bounds write

I believe simply disallowing "+" and "-" from accepting pointer types is slighlty less work than writing logic for "integral + pointer", "pointer + integral", "pointer - integral", and "pointer - pointer". Although on the other hand it means that instead of literally rewriting "a[i]" to "*(a+i)" in the AST, one has to write a separate logic for array accesses so... okay, so it's exactly as easy to compile ("as hard" technically works as well, but since it's actually rather easy, not hard, I've chosen "as easy", hope you don't mind).