The SMTxFE teaser shouldn't have been shown in the first place due to its vagueness and how misleading it ended up being.
Truly a shame, as I was quite interested in the game. Even the first trailer, though unexpected, had me giving the game the benefit of doubt.
Then, the remaining news came and my hype died down completely. The game still has some interesting ideas, though, such as exploring two different worlds, one being modern Japan (SMT) and a fantasy world (FE). However, the main premise in regards to themes is so far off from both SMT and FE that it became something completely different and alienated both fanbases.
In its final state, it's just an RPG about Japanese entertainment industry with some Atlus RPG and Fire Emblem elements tacked in for no reason besides being tacked in because they had promised to make a SMT and FE crossover.
J-pop and such aren't bad themes by themselves, but it's not something that has any relation to SMT or FE. SMT is about law and chaos, fighting demons and divine entities. FE is about fantasy worlds with dragons and also has divine entities.
The fantasy and supernatural themes would have made a better core theme for the game than J-pop of all things. Again, it's not that J-pop isn't bad by itself, but it's out of place in a game meant to crossover two series that have a main premise of fantasy and supernatural.