Oh boy They're pulling GX characters into Arc-V
I'm already suffering going through Zexal because of this damn arc, now they want me to also watch GX? My body is too frail for this
You're not missing much if you don't want to watch them. GX was mostly "Judai saves the world...then again...and again". You can wiki Edo's page but he's the "cool-er hero user" who likes D....what? that's the name of the archetype! .......Asuka? Oh yeah! she WAS in GX. I'd say maybe watch S2?
Zexal is mostly filler build up for the final arc. Kaito forgot to pay the O2 bill(he gets better). His dad Dr. Faker and his brother Haruto? they ded in this timeline/universe You can skip a lot of episodes and not be completely lost.
Shorter answer: GX Edo and Asuka didn't really do much, so it's probably all new. Kaito, while important in Zexal, his role is different in this Heartland.
Well it's not like i think i'll completely miss on their characters if i don't watch their series, Jack and Crow were pretty much the same thing and had their background explained and all, it's mostly the fun factor of "Oh yeah i know this dude! Wonder what he'll do here!"
Also i don't wanna miss the little stuffs, i mean it's just briefly but we did get a reference to the Crimson Dragon and that purple haired imp, also that guy using the earthbound gods i guess
Plus, going through Zexal may be a little painful but it makes it worth it when i remember that every single one of those XYZ scums will scream in a burning agonizing death when the Fusion bros arrives GO OBELISK FORCE