To start, the current version (0.2) of the scalar type hints RFC is the correct way to do it, if we really want to have two modes (whether declare(strict_types=1) or <?php strict doesn't matter a lot here).
Type hinting in general is useful, no question. We can guarantee in the function body what we types are working with. That avoids bad surprises like working with a non-numeric string when we expect an integer. Very nice.
But two modes? Why? What issue are we solving with strict typing?
Only equal parameters can be passed in. There also a "numeric" type hint was proposed, to solve the issue where we just want a number.