The only common thing about all these subs is that that are unconventional. A fighter with runes. A necromancer rogue. A fiery pet druid. A chaos magic barbarian. Etc.
It doesn't fit any particular setting well. Not D&D, not even MTG all that well. You could make an argument about being planar, but there isn't a strong planar vibe coming from a twilight cleric or poet bard. Similarly, if it's MTG focused it's all over the place as far as origins; some might fit certain planes, but some do not fit any well and they don't all fit one single plane we know of.
I wager whatever this product is, it's going to be very off-kilter compared to what has come before. It's not another Xanathar book, I feel.