So it seems the OP wants chained slice-dereferencing braces to calculate a cross product. That would be very unlike anything perl does at the moment.

I don't see how @hash{@list}{@list} could work without being horribly magical, inconsistent and counter-intuitive. @hash{@list} returns a list of hash references, not a hash.

If you want to change that, you'd have to invent a syntax like %hash{@list}, which merges all the hash refs into a single hash, which can be sliced in turn.

And then you'd have to find a good way to deal with duplicates in the new hash.