I accept the 'commander' argument for Mandate of Peace since we often get more out there cards in commander only sets. But it was a fog I knew of immediately.

Looking for more recent fog effects in white, there is Eerie Interference from Sep 2023. Generally worse than Holy Day but it could additionally stop other effects such as from Guttersnipe with added benefit of not stopping your blockers/attackers dealing damage.

Two years ago (at least), we had a white fog in standard. For most of the game's history it has been a part of white's wheelhouse. I think moving out of fogs for white, would be a mistake. However, I would accept less efficient or more specialized fogs in the future (which they have done already, could just keep getting less efficient).

I'm just a bit stunned we're calling cards like Holy Day and Mandate of Peace "very old."

I don't think it was enough employees at WOTC that wanted UB over Masters is what led to the change. WOTC, being owned by Hasbro and not their employees, probably means upper WOTC management or direction from Hasbro forced the change (because of profits).

Though, I do not actually know their exact chain of command or behind the scenes decision making process.

WOTC mentioned a while ago that masters sets were going away, I imagine to fit more Universe Beyond.

This isn't the first time they've been shelved. My guess is they'll be back once we dial back from UB.

Ruling from gatherer: "For Kyoshi Island Plaza's first ability, the number of Shrines you control is checked when the ability resolves. You will still search and shuffle your library if you control no Shrines when the ability resolves, but you won't get any lands."

The second ability should work the same. The state based action will kill one of your shrines before you search. So, if you only had one other Kyoshi, then you search for one land (because of its first ability, at resolution, only 1 exist).