While Cloud Saves would be great to have, they do pose some challenges that are quite tricky to get around unless you limit other things in the game

First off, the reason why they're tricky is the ability to load to an earlier point in time opens the door for item duplication (a door that has been closed by the persistent saving feature of the new game, so presumably they want to keep it that way). With no restrictions, it'd be as easy as trading an item to a friend, then loading a cloud save where you still had that item.

So how do you prevent item duplication AND have cloud saves? Even as an experience Data Engineer and one who's also dabbled quite a bit in video game modding and design, it's a difficult question to answer. Here are a few ideas I've came up, of varying complexity, that'd solve the issue:

Only online trading:

By far the easiest way to fix it would be to implement a transactional trade system (open trade window, you both offer items/money up, hit accept, hit confirm, items received). If players have to be online to exchange items, and they need to conduct a trade, it can be designed such that a cloud save for both players is recorded just before the trade goes through, preventing players from loading a save before the trade. If internet connection is lost or a system is turned off before the trade completes, it is canceled.

This alongside removing the ability to pick up items from another player's town (can't just drop a leaf or bell bag and have another player pick it up unless they're a villager in that town), would be a rock solid method, however players lose the ability to exchange things unless they purchase online and are connected to the internet (no offline trading).

They could still allow you to visit another player's town locally, but you'd only be able to do things like gather fruit/weeds, plant stuff, pick their plants, catch fish and bugs, talk to villagers, etc. No trading, just playing together.

All Items and Bells are not saved:

If cloud saves don't record any of the items in your house, inventory, town, or any of your bells in your inventory or bank, you couldn't possibly dupe items using cloud saves.

You would lose a lot in the event you NEED to load one, but you'd also at least have a large amount of what makes your town unique, such as:

Designs, Paths, Town layout, villagers, friendship, your house, anything untradeable(bugs, fish, golden tools?), buildings, museum progress, collection log, mileage unlocks, recipe unlocks, catalog, etc.

While both work, option 2 is: