Holy crap...did people went crazy over these... I'm not even gonna bother with emotional rants, I'm trying to be more pragmatic about it. These cards are going to be in the game, period, there's no rage that'll change that, so I'm just interested in how they will affect it.
Something I was thinking just now that scares me, is how these are potentially too clunky in one place (standard) and completely broken in another (expanded). The fact that they're neither basic nor evolution pokémon means there's pratically no reliable way to search the pieces in standard, the supporter is too slow, specially in this format, and just hoping to get to them naturally as the game progresses as some people suggested doesn't sound like a good idea to me, at least in paper. It already feels like there's never enough space in lists as it is, let alone having to lose 4 slots to these, plus, the loss of consistency is not worth it I feel like. Imagine having one or more pieces Marnie'd to the bottom of your deck. Ugh, yikes. On the other hand, like everyone and their dogs pointed out, in expanded, with Battle Compressor, these feel kinda dumb. The question in expanded is: is the loss of consistency there, less severe than it is for decks in standard, enough so to make them not too big of a liability? I mean, sure, Battle Compressor helps get them in the discard, but they can still show up in your hands and just mess some of those hands up, plus, there's the same problem of like "oh, one of them is prized? too bad..." that we'd have in standard.
All of this is just, of course, speculation, and only when we get our hands on them and test them we'll have a good notion of how they actually play out in both formats. With just my instincts, at this moment, my guess is they'll be too clunky for standard, and good enough (potentially scary) in expanded.
On the issues of acquiring them, I think most people are highly overreacting. Even if they're like Vmax level of rarity instead of V level (which I think is a safe bet), they're still easier to get than the typical 4-3 V-Vmax lines. Plus, there's no reason for one card to be more valuable than the other, so people with "2 legs" will just trade people with "2 faces" and so on. At least on PTCGO it sounds super easy, I can already see the endless listings of people trading specific parts for other specific parts, I think this is a non-issue.
Anyway, I think overall, although I agree that it's not the most "elegant" design ever, I mean...it's exciting, at least for me, it's interesting to think about how could we potentially use them. I think they pose interesting deck-building challenges. The art is also dope. Also, hard to pull off or not, Zacian looks absolutely stupid, I dread the day I'll have to be on the receiving end of that.