No answer for how to make it work in MP, but for SP I'd actually like something achievable for later game that would reduce the "making the trader rounds" thing.
Taking the Skyrim approach, chews up the clock, ok. Not great, but late game when I might just be looking for that one item, I might use it.
But would prefer something like;
You travel to a distant trader and open an Account. Deposit Dukes in that Traders vault.
Now at any other trader you can open any distant traders menu that you have an account with and buy items from them, plus a Shipping & Handling Fee (15%?).
Goods take a day to arrive at the trader you were standing in when you purchased.
Could only allow depositing more Dukes into your account when at a given trader.
This basic mechanic seems pretty self governing. Early on I don't have enough dukes to deposit 10-15k at several traders. And when I am flush later on I've probably already been to each trader at least a couple times, so the drive itself isn't anything new.
On amount of early dukes; I've read posts where players are getting massive amounts of dukes very early on. I kinda doubt that will always be a thing, but who knows. Would fall into the 'don't use it if you don't like it' pool for me.
Only thing I can imagine 'exploitable' would be a bit silly; opening accounts early game with just a few hundred, couple thousand dukes in each, used to buy several traders cobblestone or food. Though Food could be non-shippable 'because it would spoil', or, to avoid that bag of worms, deem it "Fragile" so not shippable.