I find it somewhat surprising that a UK city isn't falling over themselves to bring Formula E to their streets. The green credentials and boost to tourism alone should be enough to make an easy sell. I would have thought Manchester, Birmingham, Glasgow or Edinburgh would be more than capable.
As for double headers, with the move to one car per race it's not logistically any different to have 1 race needing two cars per driver as it is to have 2 races needing 1 car with a spare so it makes sense.