Not a release cycle length problem

The reason the Linux kernel can't use this well-worn strategy for eliminating bugs is that the special economics of open source and community development don't provide a way to get people to do all that boring alpha testing

It seems Adrian complains the alpha testing part is done. What's not done is exploiting all the testing reports.

Chopping the quote where you do, it looks like you're disagreeing. The end of that sentence is "and debugging." I assume it's the debugging part that nobody is signing up for.

I also strongly suspect that in the cases that concern Adrian, the testing done was beta testing, which engineers don't find nearly so objectionable. Beta testing is where you fire up the new code and try to use it for real work. Alpha testing is where you simulate using the code, for no gain other than flushing out bugs in it. That's what's boring enough that engineers seem to have to be paid to do it.