How anybody would predict what Microsoft will do in 8 years time is beyond comprehension. Although Microsoft do publish lifecycle dates the contractual promise is the EULA which contains no such dates.
They may have problems reducing the timespan in the future because of the lifecycle statement but few would complain if it was extended.
The claim that this will be the last Windows release would indicate they may have something in the pipeline already or they could follow the Apple model and define future releases all as Windows 10.X or the like.