They made way more sense in the win95/98 era. Now the uninstallers are way more effective and the machines powerful enough to make any difference unnoticeable. So yes, commercially speaking, most of them are snake oil, but technically they are not.
I think its going to be just called 10.0.XXXX (XXXX is the build number for TH2) 10.1 is going to be have to be a bigger change than what's happening now. Possibly Redstone is going to be 10.1? We will just have to wait
Since Windows 10 is "the last version of Windows" whatever build they release will still be called Windows 10.
Windows 10 Fall Update. This is the official name of the first major update to Windows 10, though of course the OS will still be called Windows 10. In order to differentiate Windows 10 Fall Update from the RTM release, however, it will be identified as version 1511 (where 15 =”2015,” the year, and 11 = “November,” the month), indicating its date of release.