Emulsions are fine at room temperature for at least a century likely more.
This is demonstrated by glass and paper negatives and positives created over the last century.
Glass is arguably even more dimensionally stable than polyester,
yet glass negatives are completely fine after long periods of time.
It doesn't really make sense that an emulsion could "shrink" as it is attached to the base, rather than to itself.
If glass negatives are fine after a hundred years, then it would make sense that so would polyester ones.
Core-set is something that affects acetate films much faster than polyester.
Interestingly the acetic acid in acetate actually encourages the fading of color dyes.
So it may actually make sense to use color polyester film as well, even the dye based ones,
though they would likely only be marginally more stable it could be worth it.
Ya, I was thinking about that, having 3 black and white photos for each 1 color,
though I think that it's possible the mineral pigment based autochrome idea could work also.
Anything cold-stored has better longevity than anything at variable temperatures,
My freezer is pretty empty aside from some microbiological cultures and some ice,
Though I'd still prefer to keep my records on a shelf if possible, next to journals and such.
Anyways even in a freezer, polyester will live longer than acetate,
the length of time only increase by 3 per 10 degrees less,
so instead of say 40 at 20C, it's 1080 at -10,
wheras polyester is 1000 at room temperature,
so would be 27,000 at -10.
And if we are talking about lengths of time that long,
I think just some freezer wouldn't do much good,
it probably wont make it that long,
though maybe some polar cave near a glacier might.
If we're talking about that long,
perhaps it would be best to have a gum-bichromate film,
fast-setting with carbon-black pigment, for best stability.