so tighten it even more by making us declare their types as well as required,

I said above "What makes development fast is the use of the flexible scalar type". So you'd lose that, it seems to me. You'd lose a lot more, in fact. The stuff that makes Perl Perl. Even basic stuff like returning lists from functions would become (a lot?) more complicated.

so it doesn't have to be interpreted any more,

Perl isn't interpreted. Perl programs are compiled into a list of native function calls. Perl just calls one function after another:

   while ((PL_op = CALL_FPTR(PL_op->op_ppaddr)(aTHX))) {
       PERL_ASYNC_CHECK();
   }
[download]

And soon, probably

   while ((PL_op = CALL_FPTR(PL_op->op_ppaddr)(aTHX))) {}
[download]

(PERL_ASYNC_CHECK checks if a signal was received. A proof of concept was given that shows that moving it can completely eliminate the cost of checking for signals.)