awesome idea. Now that I'm thinking about your steps it makes a lot of sense to go into this direction. The stair lifts are definitely well established but I feel like since it is the only real solution to the issue at hand the prices are still beyond of what is reasonable. In fact, my grandmother has her bedroom on the second floor and she has very slippery marble floor steps and because of that she often needs help to get up the stairs. She also has problems with her ankles and her doctor tells her every time that she needs to go up the stairs even if she's not going to sleep. I really like the idea of rubber surface on the steps to make it less dangerous to slip as well. For people who live in apartment complexes with big flights of stairs, you could maybe think about adding an extra step that is extra big. That way the users could take a break there and put the stuff they have in hands down on the step as well. I really like the lego or tetris kind of system you chose, that makes the assembling easy. I think your idea has great potential! Good luck with it.