Anne Happy is getting really gay.
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.