To head off the question before I’m asked it: no, HPLIP 3.9.10 will not be in Fedora 12. We will stick with 3.9.8.
The 3.9.10 release contains a completely re-written print filter, 27 thousand lines of new code, all of it written by HP with no outside review. There is no public source code repository for HPLIP so 3.9.10 is the first time this code has seen the light of day.