So... this is basically "tribal". Would there need to be a set of "ground rules" or expectations for deck building?
Well yes, I've been thinking about that, but not specifically for Rivals of Ixalan, although I'm not convinced adding that aspect matters so much when it comes to "ground rules." This was actually material I was thinking of putting in an article, but I'd already started a different article (which is now finished and I'll submit it soon). The summary, though, would be that I've been playing a lot of Canadian Highlander at a local gamestore and that in thinking about how the their "point list" is really pretty logical and that seeing the format play out, it works better than something like a list for Legacy, Vintage, Modern, etc. would when applied to a highlander format. The cards that are problems for Legacy/Vintage aren't necessarily the same as the ones that are problems in highlander formats and, more importantly, the cards that are problems in highlander formats aren't necessarily banned or restricted in Legacy/Vintage. However, giving it some thought, I think I can spot most of the truly egregious stuff. My idea was that in a tribal format with all cards outside the tribe restricted, I could (or someone else could, or ideally a small group could) identify potential problem cards, test them, and present them to a "council" to determine whether those cards should be banned. Looking at highlander formats, of which there are a few notable ones, as a starting point, there's a fairly obvious core of broken cards that could be eliminated right away, and that would probably leave a manageable suite of cards for a council to deliberate on. I imagine that there'd inevitably be some game eventually where something questionable flew under the radar, but if even one person is looking into potential problems and reporting them to a committee, the kinks could be worked out, especially as people got more experience in the environment.
I think under a "Tribal Lowlander" setup, the more pressing issue than individual card bans would be which
tribes to ban, because in our old tribal games we banned goblins, elves, zombies, and nothing else. When we started in 2005, those were probably the only really scary tribes! But a lot has changed since then and it isn't obvious to me how many more tribes are out there that might be overpowered. There's more risk of, uh, spoiled games, involved in this aspect, I think. In part, this depends on the participants. For reasons that I probably don't need to go into, under this model I'd be reporting to the council anything I found relating to the potential to "break" tribes, rather than actually bringing such tribes to games.
I think it could work and I find the "Lowlander" concept we seem to have invented here to be an interesting deckbuilding restriction. So I was planning an article based on this, although I wasn't really expecting to get enough participation at the CPA to make such a format a reality. Thought it might be just a good analysis for the potential setup of casual Magic variants. Of course, if CPA people want to try to get a variant going, I'd be happy to work on that. My concern for that wouldn't be that the group is too small or that things would stall (which they might, but whatever). It'd be that some of the players here prefer Limited formats or formats with pre-built decks, because deckbuilding for Constructed Magic is a bit of a chore and ain't nobody got time for that. I mean, that seemed to be the biggest reason the old tribal games ground to a halt. So, not trying to discourage more games in the Games Run board, because I'm always interested in more of them, but I do see that as an obstacle, and an understandable one. If we're essentially making our own format, it also means we need to make our own Constructed decks. While I can't be sure, I think I know how decision-making processes for things like "what cards to ban" and "what tribes to ban" pretty smooth. But "how to build a deck" is going to be a hurdle no matter what.
There are a couple of other things I thought about but wasn't really going to note in the article. We'll see. A bit one might be whether/how to regulate infinite combos. My instinct at this time is to just "ban" them and go from there. I do find that to be inelegant and there are some things about it I don't like, but I can't think of a better solution and I'm kinda torn. On the one hand, infinite combos are probably just bad for multiplayer Magic in general. It's demoralizing to have a 5-person game just abruptly end because one person "went off." On the other hand, the threat of infinite combos adds some interesting counterplay and interactivity: cards like Krosan Grip and Force of Will become better because they can sabotage attempts at going infinite, and in some situations a player can see an opponent's infinite combo components and use that politically to entice other opponents to target the combo player. But yeah, right now I'd be inclined to say that it's probably just not worth it. And that's a real shame, because Tribal Game 6 was really the most memorable experience I've ever had in my entire life.