I don't think O gauge kits would be a viable option in this day and age. The design and production costs still have to be covered and skipping the mass assembly line might not save much.
Taking a look at O scale British kits in 7mm/ft for example, they go for hundreds and don't even include wheels, gears or motors.
The live steam kit approach, where sections of the project like running gear, boilers and fittings are sold separately to break up the financial load might be an option, but maybe that's too small a niche.
