You know, I'm happy to point Moose out to non-Perl hackers, it usually shuts them up about how much of a mess Perl's OO is. They tend to glance at an example and say "Oh this is nice! This actually makes sense". On the other hand "anyone installing something as obscure as Array::GroupBy is sure to have something as mainstream as Moose" sounds a lot like wishful thinking.
If you do release this to CPAN, I think Params::Validate as a prerequisite is a much more viable proposition. The fact that there's a very useful analog over in Moose land makes me think of someone saying "Hmm. I need to put my cup down somewhere. I know, I'll go out to my car and use the cup-holder."
• another intruder with the mooring in the heart of the Perl