I think I understand what you are proposing, and it seems feasible. It seems like the same concept at the Form:1 from Formlabs, only flipped 180 degrees so that instead of the build platform rising from the resin with the laser underneath pointing upward the platform lowers down into the resin and saline mixture. I do believe that this would be adding unnecessary complication by adding a third axis of mechanical movement. Also with that method you are limiting your resolution compared to using drops which you can vary the size and number of drops and the dimensions of the container can be adjusted to make it even higher resolution if the surface area is larger. A few things that you might want to take into consideration if you attempt this are the displacement of water caused by the lowering build platform and lowering mechanism, the materials used for the platform and mechanism so as to prevent corrosion from immersion in salt water, and the vibrations and disturbance to the surface of the resin caused by each lowering. If you were to gear down the stepper motor you should be able to increase your resolution in the z-axis with your design. A possible benefit of your design is keeping the level of the resin at about the same height, thus keeping it as close to the focal point of the laser as possible. I do find your concept interesting and would encourage you to try it and let us know how it works out and how you accomplish it.