I really do wonder if this will stick or, like someone mentioned, fade away like Lost Zone mechanics did; it'll all depend on whether they make any sort of Dragon Energy card or will it just exist as a possible typing for a card but never factor into Energy requirements, etc. I miss the idea they used to have with Dragon types wherein they'd consistently have unique Energy requirements -- Salamence always needed some combination of Water/Fire, Flygon Electric/Grass, Dragonite Water/Electric... You also have to consider that more often than not each TCG set tries to have at least one representative line of each type, remember when there were few Electric types and the same few Electric Pokémon got ridiculous amounts of reprints? I can't see them wanting to introduce another opportunity for reprint fatigue.
If it really does end up a fleeting gimmick, I could see it sort of building off Holon/Delta Species (and others) as a precedent, with various Special Energy cards and Holon Transciever et al. equivalents except that now it has a specific Energy type to support instead of a Delta symbol (or an Owner's, Dark, etc). That would set a novel precedent for even more interesting things, like a literal 'Crystal' type a la e-Card, but I have to say I'm surprised they're doing this before revisiting typical tropes like TR/TRR-style Dark Pokémon, an Owner's set, or even revisiting Delta Species if they think the format needs a shake-up with respect to Type balance.
