I personally wish we had some better support for either earlier or later start dates. I loved playing in 1399/1356 in EU3. The Ottomans aren't completely assured to crush everyone, the Golden Horde is the scariest thing ever (but will basically always implode), France starts in a more precarious, shattered position and has much more to do, etc. There's just a lot more dynamics and you end up with some truly interesting, history-defying scenarios.
Meanwhile, with Eu4's mechanics and start dates, all the major stuff basically always happens the same way. The Ottomans always expand in the same way and are always successful - they eat minors, byzantium, more minors, and then slowly snake their way through the mamlukes. England always loses their early war with France, eats everyone else on the isles, and then sits there doing nothing for the rest of the game. France wins that war, but has ended up nerfed down enough that it basically only sits there in fear of the Emperor until the end of time, sometimes having small skirmishes with Castille. Bohemia does virtually nothing, ever. Their main purpose seems to be trying to snipe the crown from Austria, which, if it happens, makes Austria (and the rest of the HRE, really) do nothing, too. I think the way they set up the major powers in this game needs some looking over, as the fact they are either set up for near 100% success (like the Ottos and Muscovy) or 100% stagnation (like Bohemia and England) makes everything else in Europe turn out the same, too.
The game has certainly come a long way since EU3 when we talk about how interesting it is to play outside of Europe and Anatolia, but inside it's stale.