I feel the two biggest factors that will affect how data transfer is going to be whether FFVIIR stays exclusive to one console generation or if they will make say Episode 3 or 4 a PS5 exclusive. This probably won't be a problem for the PC version, but if later episodes ends up jumping to the next console cycle exclusively and depending on how Sony, Microsoft, and SE work around player profiles for their systems, I can see a later entry dropping data transfer but maybe just giving you a minor bonus if you had played the earlier games, but not do a pure 1:1 transfer.

The other factor at play here is what Fynn brings up, which is the mechanics of the game going through changes making certain items and abilities impossible to translate and rectify. I already see Episode 2 is going to make some gameplay changes based on fan feedback from the first game, and depending on how equipment, materia, and abilities work in the first episode, we can see some major changes that will make a direct transfer also not work too cleanly. Though in this case, it will probably be more of a case by case scenario where things like Summons getting nerfed between entries, or changing how limit breaks work. This area would only become a real issue if SE chose to delay an episode to overhaul the mechanics, which will really only happen if the game gets some severe backlash about the gameplay.

Course, the smartest move, and ignoring what I said above, would be to simply have the games have a level cap for each episode for the characters. Equipment shouldn't be too much of a problem, though I imagine Episode 2 may start you in a default mode, and than after the intro section, let you have access to all of your extra gear and leveled up materia after a certain point.