They could be applied easily, multiplayer is not a barrier.
If anything, what you suggest is that there is an even greater need to improve inventory management in multiplayer.
When you play MP, would you rather sell a great item for 20gp or give it to your comrade who will win the party more success with it? I support my party. Not everyone is a scoundrel IRL.
Ehmmm... no. Allow me to disagree.
Looting/buying/selling stuff in a multiplayer game (especially in a competitive campaign), only to have the aforementioned something shared with the rest of the party or - even worse - automatically assigned to another party member, would piss lot of people, me included. Pretty sure about that...
