Ok, so thought dump of previously discussed stuffs:
The "kills every player on the wagon mechanic" is actually pretty firmly protown, because while it may be difficult to organize they are in fact additional town controlled kills. Also, the mechanic prevents a mafia quickhammer from taking place entirely. Vengeproof maker is roughly analogous to a doc shot (for both factions), and the vengeproofs should never be on wagon because of that.
The "wagoners all die" situation is particularly interesting in endgame, so it might be better to have a "Eliminate all mafia by Day X/Have a Mafia member alive on D X or nothing can prevent the same" win condition instead of standard wincons. If the numbers are 16:3 that's 19 -> 14 -> 9 -> 5 -> 1 with your proposed numbers for wagon sizes. Mafia can potentially have inevitability after 3 elims depending on Vengeproof participation (even with a mafia elimination, because 3v2 means all town have to be on the mafia wagon to win and if the vengemaking town is dead at that point it leads to a 1v1) and that's a little scary, so depending on EV numbers/ preferences you might prefer a "Have a mafia Majority on DX/ Prevent a mafia majority on DX" split to encourage mafia using their vengeproofing proactively.
My guess, without looking at the actual numbers, is that this is probably somewhere in the 60-65% EV for town range, and nightless tends to increase that. With that said, I don't think that the game is unrunnable as an experimental and it should go fast enough/meme-y enough (see Exploders mafia) that a little bit of townsiding is actually prefereable.
The actual vengeproof role is problematic if it's nightless as it becomes a functionally un cc-able full BP IC. (If mafia cc's then they die immediately after the vengeproofmaker flips)
I'd propose this as a 16:3 with just the vengeproofmakers and try to run it as an experimental just because I'm fairly doubtful that EV is going to be a good metric for how the setup actually plays anyway and it seems like the kind of game that will both fill and end quickly so you'll get useful information on how it plays out anyway even if it's not immediately the best setup ever.
A couple of updates: the vengemechanic is less so townsiding with the overall setup being nightless, so the claimed vengeproof being on wagon is not actually an issue. The vengeproof-izer should claim D1 and sets up either a conftown or a 1v1 that scum have to commit to on D1 and the vengeproof is functionally just a conftown scum can never answer, which means those roles probably aren't great inclusions in a nightless without scum having some method of dealing with conftowns (1x dayvig? Could have potential as a claim deterrent that creates interesting interplay with other players who don't flip with the elimination.)
I do think that this is likely within the realm of playable as a 16v3 with the suggested wagon sizes, but I also think this setup favors Blitz/marathon/F2F style play, so would suggest short deadline runtimes.
