An issue I see with this is mixing/contaminating resins. You use resin A to start a build, it gets to a certain layer where it would stop, the 3d print still has Resin A coating it. Then you take out the tray with Resin A on it and load Resin B tray. Then continue printing the model in the new material, the resin A that is still on the model mixes with the resin B (however little amount it is, but it would still contaminate it) It's not like a FDM printer, where it lays a layer of plastic, remove the filament, and lay another layer of different material on top, those don't mix together. with DLP printing you are submerging a model, that is still coated in resin and could affect the new resin it's being dipped into.
