I really doubt it will be done in an official capacity at release when they've indicated that there will be fewer playable starts, considering that it is a lot of work to fill in the history files properly for late starts; you can't just add the characters that are supposed to be alive in a given start if you want to maintain proper dynastic connections, regnal numbers, and the like, which means you're going to have to add a ton of characters between whatever the preceding start date is and the new latest possible start (and if you move past 1337 the CK2 history files won't be very helpful).
Given how much work it is, I don't think the chances are great we'll get it further down the line either, but that is harder to say for sure as CK2 (and other PDS games) got quite a few things later on that would have seemed unlikely at the start/an earlier point, and I'd say that later start dates probably are more likely to happen than earlier start dates even if dates between existing start dates (say the return of IC) might be more likely than either since at least some of the work needed for that will have been done in advance.