I'd also recommend having Jude's sprite change as soon as you start pressing a key, I didn't think anything was happening at first as it took me a bit to see her weight meter on the left. (And agree about the option to swap the W/S, I'd also have the arrow and numpad keys also mapped to the same corresponding WASD key set.)
I do see the idea about the different play styles, but it was a lot of brain power to coordinate all the controls. I'd just get rid of Space and have it be pressing 'D' again loads the worker into the elevator. i.e. If any workers with boxes, D puts their box in the elevator, if all empty-handed workers, D again loads one in the elevator. Then this is consistent when they're on an upper floor too, just press D to load them.
The balance of the weight is a bit trickier too to align the elevator to the floor, it'd be nice if there was a bit of stickiness at each of the floor stops.
It'd also be nice to play with a mouse, just hover on Jude to fill her up and click to drain her or something. Then just click on the workers to have them drop their box or get on/off the elevator. Would make it interesting having to move back and forth between Jude and the workers to control things.