No. I dont believe that to be the case. In fact Ive seen it stated quite clearly on p5p that this was a misinterpretation of something Larry said once and that it has never been true. Perl 5.10 is going to be Perl5, theres no intention of making Perl 5.10 anything more than a better Perl5. Perl 5.10 may have some Perl6ish features, and it probably wont introduce any new features that directly contradict Perl6, but its Perl5.
What people are doing on Perl 5.9.x is to make a better, smaller, faster, more efficient, more convenient Perl5, which is actually in my mind a direct threat to the Perl6 project. The better Perl5 gets the higher the bar will be for Perl6. In fact I suspect that unless Perl6 represents serious advantages over Perl5 for the Perl5 feature set that Perl5 will never be replaced by Perl6. Instead I expect that what we will see is a bifurcation, with both continuing on to have long lives but for two mostly different user communities. (And IMO we are already seeing this bifurcation occur with Pugs).
You're a strange one. No one has said that perl5 will be anything but perl5. However, perl5 is a moving target that just happens to be moving towards perl6 by incorporating features that have been vetted in pugs or at least semi-specced in a Synopsis or two. Does that mean that perl5 will become perl6? Certainly not! But it does mean that the conceptual gap between the two will be smaller. Ergo, future perl5s will be stepping stones between the perl5 of today and the perl6 of tomorrow.
I agree with most of your second paragraph although I don't view perl5 as a threat to perl6 but rather more as gentle but firm encouragement to do a good job. Your comment WRT separate communities is something that only time will tell. Right now, it's entirely the case for me. I participated in pugs early on, but when I'd rattle off a perl6 answer to a perl5 problem at work (unconciously for the most part as I was thinking in perl6 quite a bit), it became clear to me that I'd need to stay away from perl6 for a while to keep my sanity. However, when there is a perl6 compiler available for production use where I can happily write perl5 or perl6 code and it Just Works, then, I think this bifurcation that you mention won't exist. We'll just have to wait and see (or take action to ensure whatever outcome we desire ;-)