Hey there,
I think it will be an awesome feature if you guys allow this event across servers, since lots of friends have roots on their servers and I strongly believe this will even make activities across servers more enjoyable without ripping persons out of their favorite FC's or having the need to demolish a house or a FC to marry someone they met in another server.
Clear example is two successful FC owners, do they have to delete his/her own FC to marry their beloved one? So all his/her friends have to transfer servers as well so the FC remains together? I think is an unnecessary ordeal, imho that is.
I believe this measure won't disturb game balance, probably is a nightmare code-wise but I know you guys in SE can do it!! :3
Regards.