I have always envisioned Mantis isles as place apart from Rokugani traditions. More laid back.

even had a player once making a Ronin inspired by Mugen from samurai champloo (who's from Ryuku) coming from Kyuden Gotei.

I need mantis to stay of the big guys boards to get me brash heroic daring dos as much as relentless bastard pirate

I can't imagine them not adding factions to l5r, it's such a core thing. Scorpion, Shadowlands, Brotherhood, Yoritomo Alliance, Toturi Army, Spirits, Ninja, Naga, Ratling, Hare, Spider, Mantis, Fox... AEG added a new faction within just a few sets and never looked back.

And I've only really played Warhammer Invasion, but it and GoT both added factions. I don't think we should hold out for 7 factions to be the cap.

I think FFG would be justified in adding factions but they should be careful in doing so. The enumeration of factions, especially if they are not developed enough, or not thought through properly, can leave some weird hangnails in game design. A lot of the factions in L5R were also dropped later as they were either seen as no longer relevant, appropriate, or just replaced (Scorpion to Shadowlands to Spider). Also, if you add a new faction and people get attached to it and then remove it later it can miff some players who get oddly nostalgic really quick (So many people pined for Ratlings as late as Ivory Edition.)

Not categorically opposed to Mantis, I'm just wary of handing out new niche factions like candy or just to mollify a petulant player base. The player base ought to have a say, but there should be good story and game design reason for it too.

Otherwise, Veritechs start dropping into Chi-town and dukeing it out with Saiyans. I don't think anyone actually wants that, no matter how much they protest the opposite.

41 minutes ago, Aedo said:

Also, the idea that mortal man can basically break ranks entirely and shove his way into the samurai caste would make the Mantis a major rallying point for any Ronin uprising in Rokugan and the Mantis would be flooded with requests to swear fealty.

Just as a side point, because I also saw this come up in a discussion of the Twenty Goblin Winter: ronin are samurai. They're samurai without a clan, but they are definitely members of that caste, not heimin. There are various precedents (at least in old canon) for ronin being given chances to swear fealty to clans; heimin becoming samurai are a different and much less accepted matter. (Old-canonically, it's mostly Toku + the occasional Twenty Goblin ashigaru + "hey this peasant can speak to the kami clearly they are actually of samurai lineage." New-canonically, the Dragon are messing with that a bit more.)

One of things I liked the most in our RPG setting was introduction of the concept of Scorpion gathering "worthy" peasant children into remote orphanages which functioned as a secretive schools and putting them through brutal indoctrination and training that left only few alive, whose final reward was becoming Scorpion samurai.

And also probably a ninja without the theoretical baggage of loyalty to his close family and personal wealth and ambition to pursue.

Thinking about it now in retrospect, "Monster" is a great inspiration for this kind of thing.