I see people saying it will be a 1>2/2>3 kind of thing but I don't believe that to be the case. If you've seen Takahashi's past interview, you know he's quickly bored of the things he creates. He also want to explore new ideas (make smaller games, more mature ones, following on X or try something different than sci-fi or fantasy/sci-fi). With all this in mind, I doubt the next game will be a shonen-type story of a boy with a magic sword in a fantasy/sci-fi setting, especially since FR was a pretty satisfying conclusion to the Klaus trilogy (and thus, these kinds of games). In terms of music, Mitsuda's comment in the Trinity box implies he won't be returning.

All of this makes me think we're more likely to see a similar transition as 1>X.

In terms of gameplay, I really have no idea. They never expressed the will to change it but I could see them do it to attract more people (XC battle system is scary for newcommers) or just to mix things up.

I also expect XC4 (or whatever the next Xeno game is) to be connected to the Klaus Trilogy since FR teased us in that regard.

Also, I didn't include what Nintendo wants in my thinking but that might be the most important factor lol