Here's what I'm thinking-
V Pokemon are clearly just GXs without the GX attacks. Part of me is thinking the V-Max mechanic is going to say "You can place this pokemon onto your (NAME)-V. This Pokemon has (added effect) for the next three turns. After three turns, discard this card from your V pokemon. Maybe an added attack or something. So it'd have the user consider when and when not to add their V Pokemon-Go all out, or, in other situational circumstances, wait on using it (Akin to waiting on using a Shaymin-EX, or a Lele/Dedenne I guess in these new-fangled days). At least, that's how I'd try to add Gigantamaxing into the TCG. It has to reflect the game's mechanics and I can see this being a possibly fun method in doing so.
But whatever the case, black borders are absolutely gorgeous. I'm interested to see how they'll end up being as collectibles.