From what I know, Paramore and PWT are still friendly with each other.
I think the fact they are the two main acts on that day, the GIAN organisers will block PWT from playing to prevent loss of sales.
And from the friends-with-bands side of things, MAH (why do I always go back to them haha) are also friends with PWT so there is a similar link to the SYG one you are talking about. Albeit a little more direct.
The more and more I think about it, the more and more I'm feeling theAudition.
Dream Scenario: Valencia (L)