about Microsoft's ability to support Windows 9's expected rapid update pace."
I don't think this stuff is expected to go any faster. To be fair to microsoft, the frequency of updates is already pretty respectable (latency and quality on the other hand...). The rumors are that MS will start mixing in functional changes more. Of course this seems like a mistake, their competitors really aren't mixing it up much on the fundamental level anymore (Google churned pretty hard because they needed too, but Jelly Bean seems to have marked where they broke out the functcion).
Microsoft is only bested on the 'faster' (latency and frequency) front by Linux Desktop distros, and see how much that has made people in the wider market care. It's a shame because Android updates are pretty infrequent *and* get deployed extremely slowly. This means a great deal of mobile Chrome browsers continue to have SSL vulnerabilities, mitigated somewhat by most reputable servers having addressed it on their end. If MS was botching a security update that badly the community would be all over them. Though again, the wider market doesn't really care except to be pissed at having to deal with frequent update related interruptions (where again I think linux desktop distros seem to have the right balance of availability but not being so heavy handed).