yeah.. i hate to buy a license only for mc16 to be released a week later...
Normally they backdate the process by a reasonable period, when MC16 is close to public release. Meaning: they just say after the fact, "anyone who purchased after X date, automatically got a MC16 license and just didn't know it at the time". I don't know for sure at all how much it means, but we haven't even seen even one beta yet, and they're still working on MC15, so we're probably not
that close.
Even then, there is often (but not always) a period where the new version is under active development and can change quickly, which makes it hard to rely on in a "production" environment (though MC15 never went through a serious "unstable period," that I remember anyway, like some older versions did).