pretty sure with some sleuthing
we might be able to set up a GBATemp StreetPass Relay Station
Actually its rather easy to turn any router into an access point for the 3DS.
Should be a thread on it here on GBAtemp, is where I first read it.
Its very easy, just take an extra router rename the ID correctly and turn off security.
However the relay might be more like a ghost feature than a relay between two areas.
Like for instance the 3DS sends location and 3DS mii data to a server online through the access point then it'll relay that data back whenver a 3DS is in range and checks that location for previous mii data.
So 3DS A goes to Starbucks at 7am then leaves, later 3DS B visits at 1pm and gets Mii data from 3DS A by checking online. Perhaps that would last for the whole day or so.
Knowing Nintendo I'd bet they'd do something simple like that rather than do a live relay.
On topic though, a Taxi service would be nice if it could be done safe and professional enough. However I think the risk is too great for the average 3DS owner so I don't see it taking off.
Best to wait for more options I suppose.
Might be a way to make an online relay system even if Nintendo does the one up top. Just need to intercept the transfer and reverse enginer the way the server works.
So never know just gotta wait and see.