Well, the still-to-come Dragon Quest crossover event is being done in ARR for a specific reason, like the current FFXIII and upcoming FFXI crossover events - as part of the DQ series anniversary. So I guess it is possible if the Chrono games reach a similar milestone, but otherwise it's highly unlikely.
(And as for my earlier reference to Sonic and Mario, yes I know a lot of spinoff titles now feature the two arch enemy mascots together but I was referring to 'old school' Mario and Sonic games - Sonic in, say Mario 64 or Mario running through the original Sonic game just wouldn't work.)
