I was thinking the same thing regarding the build number.
Note that the update isn't even in the Windows Update Catalog. The same conspiracy theorists who dislike the telemetry crap must be...
I would guess that the final build would be say build number 14400. When the RTM/v1507 came out  there was a jump in build numbers to something that had a good ring to it.
I would guess with the preparations needed, a final AU build will be out within the next 2 weeks. When build 10240 was released it was actually 1-2 weeks prior to July 29th, 2015.
Well, in Windows, the PST may disappear but it is still using storage in Outlook [or otherwise] to store your mail.
Sticking with IE11 and Firefox as a backup. No Chrome for me.