Having run a shop and been involved in exhibitions for many years so know how they work. I would not expect shops to pre-buy items, but could take orders. It is the norm for quite a lot of the models available traditionally, but with some of those there is no guarantee the item is actually available. Ordering to request 3D printed items will not cost the shop anything up front, as the customer has ordered it(possibly with a deposit) and delivery is less than 2 weeks. One issue might be customer's rights to return items if they change their minds.
Exhibitions, I have already included info about my 3D printed items alongside model railway I am exhibiting and had very positive feedback. I offered a workshop/demo for the next show to one exhibition manager and he said yes. If anyone without internet asks I can always offer to get items for them, I have leaflets, including one which shows all you need to start up.
Model shops, the future. This is the big problem for the hobby, as it needs that presence on the street. I think 3D printing could actually help here, as it would be possible to use a very small , almost kiosk sized unit to operate from. A lot is changing very fast, and every potential opportunity needs to be looked at.
Narrow gauge Francophile interested in 1m, 60cm,50cm , 40cm and smaller gauges . Build in scales from 1/6th to 1/24th. Also 1/32nd and 1/35th using 16.5mm track to represent 50cm and 60cm gauges. http://www.rue-d-etropal.com