OP here :D
SpeedX 3D looks really cool! Didn't know about it and it has something satisfying/special. But its not available anymore or at least I wasn't able to find it :(
Thanks for your suggestions!
So some ideas are:
Walls. Could move left/right or up/down and come from the sides or ceiling.
I think walls from the ceiling would block to much view from an art point of view even if its slightly transparent.
A wall where you need to jump on 2-3 Cube first to be able to jump over the wall.
Sliding "chunks" of 1-3 blocks that are moving left/right where you cannot jump over.
Rotate like in Inception.
I think this would break the grid based left/right movement but I will think about it.
Lasers.
A rotating laser (x rays, circular array, rotating) and maybe block 4/7 or 6/7 lanes with vertical lasers.
Changing gravity.
Tested this already and it was just weird to be at the ceiling but nice idea :D Had this in my 2d platformer and it was a really cool mechanic.