Both are highly unlikely unfortunately - the Chrono games have been kind of ignored by modern SE for some reason and are just.. there, and Xenogears has the whole issue over IP rights with Monolithsoft, so that is even less likely for a crossover.

I mean, we sort of kind of have a Xenogears reference in the game already with Gaius's Legatus armour being clearly based on Grahf, but an actual crossover probably sadly won't ever happen (it doesn't help that most crossovers tend to be connected to current games or licenses, not past ones - this is probably why we haven't got a FFVII crossover event for example despite it being SE's most popular title and the personal favourite of Yoshi himself - so that's another nail in the coffin for this I'm sorry to say.