IF that is the case, it's a rather bold move by the game designers, but in line with a lot of the recent scholarship on the plagues and their effects. We shall see how gamers feel about starting the game by losing a large percentage of their population in every province!
It would not be quite as bold if 1337 was not the only start date. I understand Paradox has analysed player data to find out that few people (relatively speaking, I'm assuming it's still quite a lot in absolute numbers) play anything but the 1444 scenario in Europa Universalis IV, so that it doesn't seem worth the trouble to put lots of work into additional scenarios. It's hard to argue with that, and it's not hard to see the downside either:
(1) From all countries becoming playable in Europa Universalis II to the attention non-European countries have received in the various expansions to Europa Universalis IV, the game has become such a rich simulation of history that it seems strange to narrow its entry to such an early start date. Sure, the game lasts 500 years, but funny things tend to happen in Paradox games once the clock starts ticking. Just the option to put yourself into the world of 1492, 1607, 1701 or 1776 as you know it from history books (more or less) was part of that richness, and I suspect it will be missed not just by those to whom browsing the pages of history in the main menu was already half the fun.
(2) For all the variety offered by Europa Universalis IV, the Age of Discovery still feels like the heart of the game. Even if I don't play a colonial game myself, some of my neighbours will and the first 50 years after a 1444 start feel like the prelude to a game that really gets going when Columbus & Co set sail. If you look at it like that, 1337 means a really, really long prelude. The Age of Discovery will wait for those who make it through the 150 long years of feudalism and plague, and it's unlikely to resemble the familiar world of 1492. I would have been thrilled by a 1337 scenario in Crusader Kings III (really happy they added 1178) or even in a game about the 100-years-war (you don't have to call it "Two Thrones Two"), but if Europa Universalis V can only afford a single scenario, I would have preferred 1453 or even 1492.
(3) This is more speculative, but maybe additional start dates would also help with playtesting for the later stages of the game. Then again, maybe player data will show that relatively few people finish a game anyway. Sounds familiar?
Second to the likely lack of decent documentation, the early start date is my main concern for what promises to be splendid game that can draw from decades of experience, passion and ambition.