Well there's three ideas behind it, with some "rules" to keep it working.
For rules, I figured Kadee #5 or #58 (or whisker equivalent), body mounted couplers only, and metal wheels (to reduce having to clean).
Mailing systems...
1. There's a "set route" 5+ people say I'll host it, and it gets mailed along, person to person, in the same box every time, each posting pics of their use. Host roads do some on site repairs from time to time. Requires each person to cover shipping costs, the last person sends it back to the home road.
2. Shipper & host & back. I send it to you, you use it for a few weeks, and send it back, I "re-load" it, then send it out again. This way allows the home road to do repairs.
3. I build & paint, you build & paint, we trade. Requires a set "value" of the car, say each buyer says, ok, Athearn Blue Box, new wheels, new couplers. This would be so that one person doesn't use a Genesis car while the other uses a Tyco, Ect.
Just the ideas for now.