Perl 5 is a different language with different features and while there are similarities, when it comes to library interface design, the differences will matter a lot. It's not implementing the groundwork, it's the interface of the framework that will need a few iterations.

Hmm, so are there any Perl 5 frameworks that would lend themsleves well to being ported to Perl 6 down the road?

Elda Taluta; Sarks Sark; Ark Arks

All of them, actually.

No Perl 5 framework I know of uses any Perl 5 features that are clumsy in Perl 6.

For example the Catalyst approach of using subroutine attributes for dispatching can be replaced with subroutine traits, so for example you could write (mimicking an example from Catalyst::Manual::Tutorial::03_MoreCatalystBasics):

method list($c) is Local  {
   $c.stash(books => $c.model('DB::Book).all);
   $c.stash(template => 'books/list.tt2');
}
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In fact subroutine traits work in Rakudo today, so the only thing that prevents people from porting Catalyst to Perl 6 is speed and development time.

I don't think other web frameworks heavily rely on intricate Perl 5 features that aren't yet in Rakudo, so there are many other possible targets for porting too.

Update: As a proof of concept I've started porting CGI::Application to Perl 6. Of course it's far from being finished, but I got basic dispatch, hooks and error mode running in with half a day's effort (and many distractions inbetween).