Well unless I miss my guess here, Joules, I think the whole idea picclock wants to try at least is to take advantage of the 3D printer's promise to make complete complex shapes with details and undercuts and then cast that in plaster, for high level rendition, but if possible reduce the amount of additional material (greensand, sprue, flasks etc) and so be able to pour into an open mold. And printed traction engine wheels with treads is what he's interested in trying, for example.
Now this sounds like a tall order, and I don't own a 3D printer and not likely ever to, and am not even a lost wax/material casting fan, BUT..........
I do think what he wants is feasible. With maybe some slight modifications.
One is that it must be a baked out lost pattern process.
Second is that it be a two part plaster mold.
Third is that it not quite be an open top mold but a shallow sprue, carved like a short funnel into the plaster. And maybe some vents.
In short, think of it similar to the way a bronze statue is cast into investment. (Mattinker, where are you?)
I think that might work to do what he wants.
Is it something I'd want to do?
Nope. I like wooden patterns, greensand, and machining.
But I'm certainly willing to cheer someone else on if that's their ambition.