Breath of the Wild and Tears of the Kingdom will have their upgrades available for Expansion Pack subscribers at no additional cost.

For some reason they didn't mention this in the direct. It's only available for the two Zelda games. Hopefully they continue this for any other games that are only enhanced with better graphics/performance.

https://www.nintendo.com/us/gaming-systems/switch-2/featured-games/switch-2-edition/