As is, it could be useful for turn based games where information is transferred only after each move. Chess, poker, battleship, etc. It would save effort over each player having to manually enter the other player’s info. If the info on each screen has to be hidden from the other (poker or battleship) you would make sure to blank the screen during transfers.
Maybe also to exchange secret information. E.g. competition hangman:
Each player picks a word for the other player to solve. The words are exchanged then the race is on to see who solves it first. For two players, there’s not much advantage over just exchanging units themselves to enter the word but if it were a 3 or more way competition you wouldn’t have to enter the same info on more that one unit.
It could be used to keep high scores in sync between units for a particular game, or even all of EEPROM to “clone” two units.
I should point out here that if this kind of thing ends up requiring that units be uniquely identified, keep in mind that there’s a 16 bit unit ID stored in system EEPROM. It can be read and written using readUnitID() and writeUnitID() and also set using the SetSystemEEPROM example sketch in the Arduboy2 library.