I mean, it’s exactly as Megamage314 said. You’re suggesting that we throw away the safe’s functionality as a mobile storage unit, and just make them chests whose contents can’t be accessed by other people. And that itself isn’t much of a benefit because in multiplayer, you’re either
1. playing with a few Steam friends you already trust or
2. playing in a public server, which in all likelihood runs TShock and allows you to protect chests anyways.
Multiplayer content is fine, but no multiplayer update should worsen the singleplayer experience. Just suggest a separate item that does this, and call it a Deposit Box rather than a safe. Also, I’m pretty sure it would be difficult to implement because piggy banks etc. are character-linked, while other chests are world-linked. A deposit box would have to be linked to both. I think it would be possible, though, given that worlds remember how much of the map each player has explored.