Progress! I have parallel universes rendering, simulating physics, and accepting input. is, of course, INCREDIBLY rough. Jumping is a hack. The 'levels' are a hack - everything is in code. The physics simulation of movement is a hack - directly applying an impulse to the player. The physics body of the player is even a hack - he's a square. Even so, I can't help but feel an incredible sense of accomplishment for what I've gotten done this weekend between homework for other courses, working, and playing a lot of games.
If the parallel universe concept doesn't pan out it's easy enough to strip that part out of the code - I remove a couple of Systems (which are just duplicated for the two worlds) and it's done. I can't say this enough - I LOVE ENTITY/COMPONENT SYSTEMS!