The main concept isn't too far from some other key platformers. Though, this would fall more into the infinite runner genre; most of which have jumps and ducks where as the gravity flipping is sorta newish baring the most discrete of infinite runners.
Since I'm a bit unclear what exact phase your going for to fit this GameJam's theme, here is a small list with my opinions:
- Assuming you are doing "Platformer without jumping", I would more turn this into a puzzle concept where stages are built to look like a platforming stage with a more puzzle mechanic to figure out how to ascend, like how they did with Captain Toad.
- If you're going for "Infinite Runner without jumping or sliding", I would look for even more ways to traverse land or avoid death. Some things like having to shoot or chop incoming stopping forces to break them before they hit you. If you're feeling a bit of change in perspective, you could have it so you change the direction of the sign or have it bend and weave. The idea of changing gravity is very similar to changing lanes in a standard Infinite Runner. Just a change in angle.
- Though if you were going for a "Platformer without collectables", I think you nailed it.