As a compromise between purity and pliability, I suggest perhaps a concept of "pioneering" apply to nudists.
Whenever a character encounters a fresh challenge that the nudist team has never done before, and they wish to bring the rewards of surmounting that challenge into the nudist team, then they must attempt that challenge nude and without outside assistance.
So for example first time nudists attempt a mission as a team without any clothes. If a nudist is absent, it is OK to play catch up on that mission by being run, wearing clothes and traveling with a pug, etc. This is pretty much how we have been doing things anyway.
Applied to factions, it would imply that an individual or small team must "pioneer" shing jae following the nudist rules. As advancement is relatively fast this shouldn't take too long... though given the greater difficulty/slower pace of nudists, may take a whole month for a weekly meeting team. But after being done once, anyone could then run their nudist there.
Seeing as pioneering here is time and slot-consuming, another option would be to rule that our team has seen enough high-level dangers that nothing shing jae offers can even compare in terms of difficulty, so it can be inferred that nudists are quite capable of beating it, rather than needing to demonstrate.
Though maybe we should wait until proving ourselves in the desert missions before getting so confident?
Another can o worms this opens up: all non-elite factions skills are avaliable to anyone who owns factions right now... it's not a very difficult quest to get to Kaineng center, and then you can buy any non-elite skill, so quite reachable by nudist rules. There might be an issue of many of us not tracking whether our money is "pure" and nudists only use money they have acquired to go purchasing these expensive skills... but then again skill points are not so abundant in prophecies and would place a proper limit anyway... EXCEPT a few of us want to use our limited nudist slot for other things since reaching level 20, losing track of how many skill points have been fairly earned while nude... ugh.
Proposed solution: either keep factions skills banned for now, OR allow all non-elite skills with no questions asked. Perhaps waiting until Ascension when almost all non-elites are avaliable anyway. If we wait for Dakk though, well I have a feeling the summer will be over.
Elite skill problem: all your rit elites are scattered around cantha. How are you going to cap them while the team is running around tyria? Should one be allowed to bring in elites that were not capped while nude? Would that significantly taint the variant as some of these caps are extremely difficult? Then again, capping elites in Tyria is an extremely time-consuming process, since many are spread out in obscure areas of the shiverpeaks that the team does not need to visit at all for story progress. We may need to rethink our elite-allowance strategy here, especially since we will be hitting the desert real soon when elites start to show up, because forcing us to cap elites we want would either be a huge time-consuming burden on the team, or else pressure us being fairly selective about which elites to cap and consciencious of team time constraints... and additionally not very flexible for guests to come and "undress" with us.