@Aurethious, I suppose I fall more on the "building around a new mega team" side of the equation, in that I don't want to exclude Gyms and their Leaders due to XY backwards compatibility.
I did have a couple challengers last year asking me how to join in, playing with Black & White, but only one who didn't have XY on hand, and one guy who with his GBC (gold? I think) but he didn't bring his link cables so we couldn't battle
I think a reasonable way to deal with it is within the Gym Leader forum, when Leaders have their potential teams on display, we can build some Leader consensus on the issue. I'm hopeful we'll be able to offer Gym Leaders a healthy alternative to their incompatible pokes, if push comes to shove.