Taking stabs at a couple possibilities beside the "it's Tag Team VMax". All anticipate we literally just get two V-Union cards, for the two different Calyrexes;
- Ice Rider Calyrex V-UNION and Shadow Rider Calyrex V-UNION are played from your hand and functionally identical to Pokémon-V. I think this is a likely possibility.
- The two V-UNION cards are played from your hand but act more like VMAX (i.e. 3 card prize for KO). I'm out of the loop on the meta right now but I assume this is too broken at this stage in SWSH block. Unless Gen 9 really is going to drop next year, it seems to early to be bringing back TTGX-tier power.
- The two V-UNION cards have to be played on top of Calyrex V; with or without some additional caveat to actually play the card. Which could include either you must discard a Glastrier/Spectrier from your hand, or you must have and also discard a Glastrier/Spectrier from your bench, or some other permutation of a mechanic along those lines.
I think it is *incredibly* unlikely we will see them bring back a LEGEND-esque mechanic.