One thing that's cool about Arduino is you can easily scale to fit your needs.
Or in your case you can scale it massively over your needs but more is better!
I am definitely in envy of this project. I have a lot of arduino stuff but it's not really expensive things like cellular shields!
Ok, some of it's rather pricey.
Anyway your scooter kinda reminds me of the BEHEMOTH:
or the older winnebiko 2:
or maybe the even older winnebiko:
Just keep adding more stuff!
To be honest, your arduino setup can probably do everything the winnebiko and winnebiko 2 could do 
(More info on the pics: http://microship.com/bike/index.html)
I wonder what restrictions and legalities there are with that kind of thing nowadays :
(Mowcius plans his next project 
)
Right. I submitted your project to hackaday
It really should be featured on there!
I hope you don't mind
Mowcius