User blog comment:SayuriDarling/The Sword of Summer Official Discussion/@comment-5984859-20150804101842/@comment-25044056-20150805005934

I predict the two worlds Norse and Greek will remain separate and the cousins will keep their mythical heritages a secret from each other at least until the series is over.

Don't get too excited about a three-way crossover. That's the sort of thing that would be very difficult to do well. If that ever happens it won't be until after the MC trilogy is finished and at least one (probably more than one) crossover between PJ and MC has been published.