So people can have your perfectly archived film after you are dead?
I used to work for a museum exhibit prep company. Practically none of the film I personally handled (about 70,000 total, almost all ranging from the oughts through the thirties, and also the original color transparencies of Ernst Haas) were in anything better than paper mailing envelopes or cardboard boxes when we first got them, and they always were printable and over all in good condition archivally speaking, although there was often physical damage. Prints dry mounted half a century or longer ago, on board that is nowhere near "archival" by today's standards (often they seem just a small step above cardboard) look perfect.
My point is simply that preventing physical damage will be the single most important factor in making your negs usable well into the future. Any sort of new plastic sleeve, whether "archival" or not, will be far better than many of the ways *truly* classic film has been stored. If you find something that is just perfect, go for it without obsessing over what is archival and what is not. In 50 years, when we are all dead, people will be wondering why on Earth we were so stupid to be putting our negs into such materials, given the new archival technology available to them. However, I'm sure our negs will be fine, on the less than one percent chance that anyone will even care to do anything with them.
I get your point, I just think that I should do what I can to keep the work in as good as condition as I can. I feel the work is important so to make archival prints and to store my negs as well as I can makes sense to me. Seems silly to me to spend your life doing something you feel is important and spend 100s of thousands of dollars on gear film etc...and then put the end result in something that is lower quality. If your going to all the effort to make the images you might as well finish the deed and do the best you can to store the stuff (negs/final prints). All of this is within reason, we should each do the best we can, it just seems wrong to me to cut corners in the endgame of your work.