It's not a bad idea, but that would mean that anyone can modify the level they are playing on the go, no?
Personally, I would be more comfortable with a separated program, something like the NeoLemmix Editor.
On a side note, I have a minor wish that's not really related to the potential SuperLemmini level editor, but to SuperLemmini in general. I really wish that the engine would support wallpaper backgrounds, that's something I'm envious of NeoLemmix, because single coloured backgrounds are starting to feel too empty. There are background integers for SuperLemmini but I'm too dense to make it work properly... There's always the good old trick of using an object as the background but it's not really intuitive.