And I think I now understand the crossover suggestion. With that idea, a submission might be a picture of some time machines together (the Epoch, the Doctor Who TARDIS, the Bill and Ted Phone Both, and the Back to the Future DeLorean, for example), right? So the point wouldn't be to celebrate a crossover that already happened (example: Lucca appearing in Xenogears), but to create our own crossover? That makes more sense.
Now that I understand the original idea, I think the two ideas could be combined. We just need a carefully vague title like "The Influence of the Chrono Series" or "Chrono Allies", but with more thought put into it because that was top of the head.