Zane & Atticus/Nightshroud should be the last of the GX + Sora, who I know is technically ArcV but I'd personally love it if he and Obelisk Force showed up to invade before ArcV's release to build up to its eventual release.
Zane and Atticus won't be the last, because there's an event for Yubel coded into the game, as well as Sartorious and Tyranno Hassleberry. But Yubel is 100% going to be revealed probably either with Zane's unlock event, or with a future "dark world" event. Because they've been hinting at them ever since the game "glitched" and revealed them
Oh right, forget about Yubel... And as much as I love their characters, Axel & Tyranno have no special cards about them as they've all been released in Packs. Letting them out as fill characters seems like a waste now unless their special abilities are completely unique. :/