Last week, Microsoft pushed out Windows Insider build 16299.15; an updated build of the previous Insider Preview build 16299.1. Considering this is the same base build, but a newer compile of it (with bug fixes), could 16299.15 become the Fall Creators Update RTM build?
The timing is certainly about right, and this would also follow what Microsoft did with the original Creators Update builds (namely fixing on a "base" build and then issuing incremental updated builds until all the blocking bugs were eliminated); and having been running 16299.15 for most of the last week, it certainly seems stable.
Microsoft's release notes for this build don't indicate it *is* the final build; but I guess we'll only learn that as we get closer to 17th October. (read the Update 2 line in the release notes)