I know that. I'm only referring to what happens if someone switches from Sony to Xbox. Will they lose their skins and stw access? Don't know, but if Gold goes away and PS+ does not, I will want to know.
I think the main difference is that you'd still need to pay for PS plus to play STW (online)? I'm assuming the STW portion requires paid online since it's not the F2P portion of Fortnite. Genuinely have no idea on this.
With regards to progress and cosmetics, all those are synced up with Fortnite servers and can be accessed on any device. No STW on Switch or mobile though.
And one more detail (that you didn't ask for): purchased vbucks are tied to the storefront you bought them from.
Eg. You buy 2000vbucks from PSN and 1000vbucks from Nintendo eshop, you don't get 3000 total on either account.
The game deducts the purchased vbucks first until they're depleted, then they'll deduct from the universal vbucks (from the battlepass or STW).
Continuing with the example earlier, if you saved up another 1000vbucks from the battlepass, on PS4 it'll show up as a total of 3000vbucks. On Switch it'll show up as 2000vbucks.
So if you buy a 1500 vbucks skin on the PS4, you'll have 500 PSN vbucks and 1000 universal vbucks left. On Switch you'd still have 2000.
If you chose to buy the 1500 vbucks skin on the Switch, you'll have depleted the 1000 eshop vbucks, and spent 500 universal, with 500 universal left. On PS4 it'll show up as 2500 vbucks left.
I'm pointing this out (clumsily) because in the event you see a good deal for vbucks on one particular platform (eg. discounted PSN/eshop codes) you need to know it doesn't stack with vbucks on another platform. If you had 1000PSN vbucks and wanted to buy a 2000 vbucks skin on the Switch, you'd have to purchase 2000 vbucks on the Switch, not 1000.
And trying to even up the vbucks to prevent confusion is a bit cumbersome because it prioritizes deduction from the platform-tied vbucks first.
P.S. I'm not sure how it works with mobile.