As you said, only time will tell, but I think we can make more or less good estimations.
First, each charater's skins will be released/changed/etc in the month they get the ability refresh with the new backstory. So only Winona's skins would be upgraded in March, the others' in the next months.
As I understand, each skin will have two variants: a regular and a heirloom variety, which would be different items on the market. Personally I expect the regular skins' prices to drop after their characters' refresh - why would anyone buy the exact same skin for a lot of money if they can buy if from Klei for a fixed (hopefully lower) price? However, the heirloom skins' prices might increase - they will be limited as they won't drop anymore and I'm sure there will be collectors who will want to have heirloom skins, not matter what they cost. Also since they'll have a higher unraveling value I'd expect many people to unravel them - so there would be always less and less of these skins. I could be very wrong here tho - but who knows? Well, we'll see it in a few months.