Getting the balance between personal interest, and commercial viability is the point. Great thing about Shapeways, as I said is that you don't have to invest the cash before selling any items. It helps if you want models for personal use, and the smaller scale models are a lot less expensive.
I have tested out one model in OO9, as a challenge and because someone suggested it, but there isn't much point in expanding range as others like Tom as well as Chris Ward are producing good models in that scale. I only produced range in 1/43 scale because I had several people asking for it and it was the first smaller scale I did, another challenge. I know how to do it, but would rather do something different.
Apart from a couple of freelance items for one of my minimum gauge projects, most of my models are of real locos and wagons. Oddly I find that easier because I don't have to think , just adapt what I see in front of me. It actually is a good companion for my creative side which I am trying to develop in my artwork. I do use creativity when building layouts to display models though.
As for Gn15, I have thought about it, but ill probably only design something when I get back into Gn15 again. I have a lot of other projects in mind before that. Chances are first loco would be a stretched version of my Decauville as I hinted at in another thread. There was also some discussion concerning a Gn15 Simplex .
But before that here is a short list of my ideas for other projects
Complete larger WW1 APA box layout in 1/35
Finish off 1/32 9mm gauge in APA box layout
!/35 layout 1940s, post WW2.
1/32 mixed gauge layout
5.5mm/ft layout, 16.5mm and 12mm gauges (APA?)
OO gauge 1970s southern electric(again APA based)
French HO standard gauge modules
and probably a few more before I get back to Gn15
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