I'm still waiting on Microsoft to explain what us "insiders" do between the time Win10 times out in April until Win10RTM ships sometime in the fall...? The obvious answer would be that the Previews will not time out until 30-60 days after the RTM ships, but it's interesting that I've seen nothing official from Microsoft about this. April is not that far away...
Best way to know is to call ms support or contact them by chat @gabeaul (if you choose chat support, kill him on the survey)
I think that the expiration date will be pushed back along the way with new releases. I'd guess that upgrading your current build to the next official one that is due in January will disarm the April timebomb and establish a new one, it's likely that this "milestone" release won't expire before August or September. It's the same with Visual Studio 2015 pre-releases, where each one is valid (licensed) for 180 days, which is plenty of time considering there is a new release every one to three months.
time bombed pre-issues of windows operating systems never expired prior to RTM. Them using the pre-releases always have/had time enough to deal with the real stuff finally in terms of activation etc.
This is interesting scenario, because Win10TP is actually WinThreshold, which was supposed to be released in early 2015 as Win8.2,,,,,,, Don't worry, they will change to a new time-bomb.
Anyway, it's just a rumor posted before Jan 15(posted Jan 8), so why not simply wait for 4 more days and see what MS says, officially.
Nah, that would be too long I believe, I just wish to show the statement that "Spartan and IE will both exist".
I still don't see myself using it, but will be giving it a try anyway. I might get surprised, but not expecting much of a rise from it.
Notice it's called "Windows 10 January Preview" in the blog, previously I heard MS guys called it "Windows 10 Preview January Update"......LOL. also, MS didn't use a "monumental build no." such as Build 10000 for just any build, Win7Beta was Build 7000.