Gold medallions could become like the new blood donation. Have an empty one, someone spends a half hour sick, and its used to heal another person.
On a darker side, this could lead to Matrix-esque sweatshops were people spend their days incapacitated (e.x. blind, sick, tired) to fill the metalminds. There would definitely need to be some government regulation in that area. Or use the ettmetal machines as mentioned above.
Our Storm Trekkers would have no communication issues with people in other worlds thanks to the connection medallions.
I can see massive pneumatic tube networks used to deliver messages by coinshots and lurchers. Like the ones in bank drive throughs but cooler and allomancy-er.