Diversity is a waste of time in this case. It's better to work on this "centralized" piece of code and create new forks based on it since the code is a damned good starting point. Don't the MooTools people have more important shite to work on anyhow rather than solving a solved problem?
The point is, Sizzle doesn't solve a problem for them. John Resig suggested to -replace- their CSS selector engine with Sizzle, not to use Sizzle in place of building their own.
You don't think ongoing performance issues and bug fixing are problems? If the MooTools selector engine were entirely bug free (I'm not claiming that it's full of bugs, just that without knowledge to the contrary I'm going to assume that it's like most other software projects and has at least one or two) and as fast as Sizzle, then yes, changing engines would be more work for no obvious benefits.
However, if they can get measurable performance improvements and increase the number of eyeballs on the bugs on that one portion of their code, then that seems like a win to me. There are plenty of other reasons why they still might not want to integrate Sizzle, but this one doesn't strike me as compelling.
My post was a rebuttal to onmouse's insinuation that MooTools didn't already have a mature, fast, & functioning CSS selector. Valerio's post quite clearly stated that, at the time, there wasn't a measurable performance improvement. Regardless of his misunderstandings about the contribution process, he wasn't ready to trade his team's control and design philosophy for dubious performance gains. That seems perfectly reasonable to me.
