My idea: a racing game featuring all four of those elements. Here's what I was going to do. Back in Full Sail, I made a cool little tile editor, which essentially made a race track. Screenshot:
Pretty cool, especially because it had a random track feature. It would create a complete random track, no matter how big the track size, the track would be totally complete. Now, it did have it's flaws. There were always little side-tracks that got made. That's easily fixable though. I was going to incorporate this into a random height mapping thing (very subtle one, to create small hills) to help give the terrain some sort of texture rather than just being all flat. I think it'd be pretty cool.
However, I lost all my source code from Full Sail (FUUUUUUUUUUUUUCK [note: Kids please don't read the previous expletive]). That pissed me off, I had a lot of good code I could look at and re-use. But anyway, so I'd have to rewrite the editor from scratch. That's doable.
I can't even finish Lazteroids 2 and i've been on that since before christmas, what the fuck makes me think I can do 4E4? HAH! (kids, don't read the previous sentence).
The point to all this? Someone, steal my idea. I won't make it, it'd be kinda cool, but I need to focus on Lazteroids 2. And if anyone has all of my old Full Sail source code, let me know. Plskthx.