This really does have a TON of design space now that I think about it. For example...
1. Batches of flavorfully similar creature types that probably could and should have been one creature type in the first place:
Sea Monsters - Krakens, Leviathans, Octopuses, Serpents (Listing every aquatic creature type would be too long, but there are already a handful of cards referring to these four specifically. What if they didn't have to list them all out?)
Undead - Skeletons, Spirits, Vampires, and Zombies (Innistrad sets REALLY want this.)
Serpentine - Gorgons, Naga, Serpents, and Snakes (What all future snake tribal should be. You could argue that hydras should be included as well, but the hydras that are particularly snake-like have the snake creature type anyway.)
(Tagging @askkrenko on this because it's really his department; his creature type guides have lots of other examples of creature types that can and should be consolidated by batching.)
2. Batches that reference a set mechanic in a way that isn't parasitic, triggering off of two generic things or one set-specific thing like historic does:
Eldritch - Eldrazi cards, double-faced cards, and cards with madness or delirium (Would have been perfect in Eldritch Moon - I think including a handful of relatively benign DFCs is an acceptable bend, as it's the only way to reference cards that are only eldrazi on the back.)
Remnants - Zombies, Deserts, and artifacts (Return to Amonkhet.) ??? - Legendaries, Arcane, and Spirits (I can't think of a good name, but Kamigawa block desperately needed this - arcane/spirit appeared on tons of cards, and legendaries really needed more payoff for how many of them there were.)
3. And finally, batches that care about specific keywords:
Quick - Creatures with flash, first strike, double strike, and/or haste (This is what Path of Mettle really needed to make the flavor click. I think flash is a better inclusion than vigilance, since vigilance often represents something other than speed. I really want to see a card that makes quick creatures unblockable by non-quick creatures for the flavor, and that's not going to happen if all these keywords have to be written out twice, so batching is the perfect solution.)
Tough - Creatures with hexproof, indestructible, and/or toughness greater than their power (Creatures that are hard to kill. Good for both benificial tribal-esque effects and specific hate cards, which would likely have to "choose a tough creature you control and exile it" to get around both hexproof and indestructible.)
This ended up longer than I intended but the point is that batching has a TON of design space, and I'm surprised that it hasn't been used before Dominaria. I'm excited to see where this goes in future sets and I would love to hear other people's thoughts on this.