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This has concerned me in the past. I have followed parrot from afar for a number of years. The thing in my lay, and completely unqualified, perspective that parrot should have done different is target a HLL from day 1. This may not seem pertinent to your point right away, but hear me out.
A great deal of would-be contributors to the project aren't interested in C, PASM, or PIR. A high level language would have opened up the doors to many more people - even if all they did was write code that exposed bugs that a much smaller population is capable of fixing. I think it would have done much more than that though. Back in the days of Dan and Leo squabbling over optimizations and features, one argument that came up was the applicability in a real language. If there had been one with a largeish code base, it would have been much easier to take things out of the realm of theory. I could go on why I think this would have been a good thing, but what do I know (really).
Ok, so far this still doesn't seem like it is on point. One of the things I have seen over the years of non-core contribution is numerous languages targeting parrot. By and large, each language had one or two individuals and the project would lose steam
What I have been noticing lately though is that the folks who have stuck around are now being very collaborative. The pugs folks are working with the parrot folks. The tools available now make contributing much easier. Also, the folks working on language implementation are also core hackers. When something is blocking for them - they can make sure it stays visible. Perhaps I am being too optimistic or naive, but I really think that what was once a problem (tangential projects) is actually becoming a great asset.
Update: I failed to mention that I doubt YAP6 is necessary. If it can produce a mostly working perl 6 implementation in a short time frame that is at least as fast as perl 5 - great. I suspect that this is not the case. I guess what I am saying is not all non-core projects are bad - but, for me, the jury is out on YAP6.
Minor grammar corrections
Cheers - L~R