The decision to have so little meld is definitely based on the idea that they wanted to include a lot of "normal" double-faced cards, since any one meld pair gets rid of two of those. However, I think you guys are underestimating the appeal will have at even these low numbers. Even if the rare meld cards don't turn out to be great, people are definitely going to try them out. For people just opening packs, seeing the back of Graf Rats will be enough to get them interested.
Though that does make me think. If Kaladesh has contraption assembling, perhaps they're using meld to solve that, or rather the same technology. There could be component artifacts that have a block of text on the back, and they are assembled to form a single contraction made up of multiple cards, with the rigger providing some extra text somehow.
I'm surprised to see Ride Down again so soon. The hat in its art looked at first like one of those conical hats, which is odd on Innistrad, but it's just a weird angle. Mournwillow's effect is a bit odd in black and green, but green has had "low power creatures can't block" in the past, sort of, and black has haste. Also, Plant Skeleton.
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Trample + the Delirium bonuses make this card. Relevant at most points in the game. Looks sweet for my Graveyard Cube.
It feels a bit odd as a mythic, but one flavor change could have been enough to justify it: make it Leatherface. Anyway, the "scry to your graveyard" effect is nice.
It feels like half this set was designed for Commander.
EDIT: Actually that dragon isn't half bad, that's a pretty good form of removal protection.
I really like Mirrorwing Dragon. It fixes Zada's problem of not lasting long enough to matter, since it affects all creatures the spell's controller controls. It will still be the only one destroyed by Ride Down, but I don't think any other significant destruction spells have conditions like that. Like Zada, use Expedite on it. There is the problem that your opponent could help out their creatures with a pump spell, but only a mirror match would probably have pump spells.