he original premise was "a game where you can see a pegasus knight at the 109 building in modern day Shibuya." This has been known since not long after the initial announcement in an interview. They went to multiple devs thinking of who would be the best to handle a game like that, and eventually decided on Atlus. They billed it in Japan as "Shin Megami Tensei meets Fire Emblem", which could be any variety of things.

In that, they've delivered on their promise. A game where you can see a pegasus knight at the 109 building in Shibuya with classes, archetypes, and characters from Fire Emblem reworked in a modern urban fantasy setting in Japan ala Shin Megami Tensei and Megami Tensei on the whole. If you actually watch the whole trailer, you can clearly see a scene that even seems to have a typical SMT post apocalyptic setting.

For those hoping for a straight crossover however, sadly that is not the case. Instead it's a more Kingdom Hearts esque "crossover", it's own thing with elements from both parts. And like Kingdom Hearts, it isn't directly tied to either series in name, so if it warrants it may become more or less its own entity.