Aren't you in danger of just further dilluting the gene pool?
Certainly... but I really don't see it as a bad thing. Each one of the efforts that tries to bring Perl 6 to life gets it from a different perspective, and the experiences from each of this projects are creating a more powerfull knowledge of the Language and the runtime requirements for it.
Eventually all this projects will implement the full Perl 6 at the same time, even because most of the people working in this projects knows each other and do share experiences.
And finally, the idea of having alternative runtimes is interesting. Let me bring one considerable difference from Parrot to YAP6. Parrot implements trace gc and YAP6 implements refcount gc. Trace gc may be more efficient and more safe, but is not deterministic. Some applications may need a more deterministic approach to memory use versus processing time.