they should create a character customization mini-game online like spore

Already been suggested and discussed actually.

I wish that had been noticed more. It might actually be something that would come to fruition if more of us clamored for it. I'm no programmer, but judging by the material I've seen from the vids, it doesn't look like it would be too difficult for them to put out there.

A long time ago, we had a discussion about different types of demos.

Some suggested the idea of the OP.
Others wanted a freerun type of game, where you were a Light and could do some SMART moves.
Third option was a demo of one map.
Fourth was an ability tree builder.
...

Most people were against some of the listed things because it would contain spoilers which would certainly be discussed on the forums.