The problem is that can of worms it opens is only how Dalton at Lynx managed to overcome them, which doesn't seem like much meat to the game itself. We already know Dalton basically had access to both the magic of the past and tech of the future, so there was one huge bump.

Lucca was not with Chrono and Marle, so all Lynx and Dalton needed to do was beat the two of them to take Guardia. So the only real question that game was just how dirty did they have to fight to win? And of course what exactly Lynx did to the Masamune. There doesn't seem to be enough here to really warrent an entire game.

CT on DS also partially answered the Magus Question, though that plot line isn't really connected to the events in Cross, and to top it all off the question of what happened to Schala is already answered, so I don't really know what they could even do if the game were to focus on Magus's story from here on out, though it may have more to it then the in between games would have.