Supposing there is a way to pause (pause) a loop, and continue it later (cont { ... }), it's easy:

my macro do_something {
    ...
}

for (...) {
    pause, next if ...;
    do_something;
}
cont { 
    do_something;
}
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For this to work, pause would only come into effect after the entire statement is evaluated. Alternatively, consider next :pause or pause :next.

Having things optimized with a simple hint I think would be trivial.

for (...) {
    notagain, next if ...;
    ...;
}
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would automatically be split.

Still, I don't think it's a problem that needs fixing. If you want to fix it, it's probably simple enough to do it in a module.

I would like the pause/cont combo, though. For many purposes, because not everyone likes to think in iterators.