I had the idea before finally making my rp to make another at the same time, with events in that rp happening across the world from the point in my first rp, and having situations and events be different enough that they'd seem to be two completely different rps whilst seeding foreshadowing elements in both that related to the other, before finally having both groups of characters in each rp eventually meet and spawn a new rp/sequel where the storylines in those two rps joined together. 

What eventually pushed me not to do this wasn't because of time or organisation, but that I thought it would be hard and unfair on players in both rps to miss out on story elements I'd be seeding in the other since I wouldn't expect them to neccessarily read the other rp, and so when the time came for those two storylines to merge into one, people would just be plain lost and confused.

But it was a neat idea.