The analysis of the letter writing feels compelling that it's Douce trying to obfuscate his writing. The timing lines up with him mailing from Florida, and the letters have been wheeled out only when they strategically think it's best, rather than parading it around everywhere shrieking as they would from such a powerful gotcha as getting actual death threats mailed to them.
I'm convinced this is a gay op because it simply doesn't line up with being a hyper autistic ISWV fool. They're asking us to accept this:
1 - An ISWVer who's so autistic they look up the doxes for very specific KV members (but not too many) which most benefit from getting death threats - including for some baffling reason Renfamous but not Hanleia or Beth?
2 - Said ISWVer is familiar enough with KF and on top of things so that they present themselves as if they know the memes and common insults toward the various people they're targeting...but they get them all wrong. 'Harvey Weinstein' and not 'Harvey Weebstein'? No mention of sacred lotion? Fire crotch?? Weak, childish vague threats that aren't even lurid?
3 - Purposeful attempts to make the person look unintelligent. Not only do they boomer through buzzwords or weeb wars memes like someone who sort of (but not really) knows them, but in multiple letters they scratch out a word in their chicken-scratch pen. They can afford to mail several letters across the country simultaneously, but they can't afford an extra page of notebook paper, during Back to School season, when you can get a notebook for literally 20 cents?
4 - Notebook page to make them look young, poor, and dumb, instead of printer paper? Plus, handwritten letters instead of printing it out? This person is meant to be someone who's plugged into the internet and anime so much that they're willing to send death threats to random people over internet anime drama, but they don't print out their death threats in bold text on printer paper, where they can backspace away any errors and won't have handwriting to identify?
5 - They have the handwriting, budget and thought processes like an angry child, but the ability to function like an adult in researching doxes, (sort of) keeping up with the drama, putting together threats, and mailing them all at the same time, knowing not to include a return address?
I think Douce is the most likely person who wrote it, but it's definitely a hoax created by KV's side with the knowledge of those who received the letter anyway. It's telling that only Lauren was willing to take the hoax far enough to actually get the USPS involved just to prove she's legit.
Here's my theory:
MoP sent his email on Sept 5th, and was stupid enough to send a death wish that could be interpreted as a death threat. A bunch of other people around this time started harassing Chupp on FB and basically having a little meltdown. Chupp also reacts with paranoia to it and immediately orders an emergency hearing about it
Doucette, Renfamous, and Marchi (at least) see this and go "I hope they'll send us some, we could really use that to crank up the fees requests and milk some more victim points out now that we've 'won'." - To their disappointment, none come.
Luckily, Doucette was scheduled to go down to Florida on a trip no one knew was happening, because he was planning to surprise propose to his girlfriend before the hearing on sanctions would be done. He travels down to Florida about Oct 5th - which I think is the day of the mediation? Before anyone could have any news about what the results of that mediation was? - and writes up those letters, sends them out, and then immediately starts teasing them when they come in the mail. Lauren races out to get hers 'certified', and Marchi immediately whips it out in the hope of cranking up her fees.