I wasn't actually expecting a hotfix for Linux (previously they were Windows only) so I don't have a lot of answers available off the top of my head. I suspect the answer to most of your questions is "because it's our first Linux hotfix"
Presumably the signature is missing because it *is* a hotfix driver. If the driver had been fully QA'ed it probably would have been shipped in place of the standard Cat 9.12 driver. If we are going to continue to provide Linux hotfix drivers then we probably need to find a less annoying way to distinguish between production and hotfix drivers on user systems.
Remember that XvBA hasn't actually been *released* yet, the work-in-process code has simply been *discovered* and some people are using it beneficially.
There used to be two Linux-specific teams - one under Matthew focusing on the core X driver, and one under Larry focusing on customer and distro issues. For the moment I believe Larry is managing the whole group while we figure out whether to replace Matthew's role and leave the org unchanged, or to shift more of the Linux responsiblity into the core component teams which handle cross-OS development.