[yor]

You might be interested in the Specialized Turbo[1]. It's an improvement over the Greyp G-12 with respect to every criteria you just mentioned.

[1] http://turbo.specialized.com/

[Fuzzwah]

Looks cool, but I have to say that the video on that site did pretty much nothing to explain to me what the bike is all about.

[yor]

You're right. That's a fantastically useless link. Here's some reviews:

* http://mashable.com/2013/09/04/specialized-turbo-review/

* http://reviews.cnet.com/search-results/specialized-turbo-ele...

A little tinkering with the crankset (which, unlike the cassette, looks accessible and nonproprietary) and removal of any speed limiter that might be in place could make for a 50lb machine that easily tops 30mph at a comfortable cadence.