I've always thought about incorporating a conventional dryer system into a front load washer platform. That is, having a submersible heating element around the back of the outer drum, in a similar manner of how GE and Frigidaire constructs their dryers (albeit, the elements are exposed nichrome and would NOT be a good mix around water!). This element could also heat water during the wash cycle. As for venting, a duct at the top of the outer drum connects to a small centrifugal blower, separated by a lint screen which is pulled up at the top.
As for the vanes in the drum, they would need to be deeper than what is typical in domestic FLs so that the laundry tumbles well as it should in a conventional dryer. I would imagine that deeper vanes would enhance wash performance as well.
I don't know how a gas-powered dry system would be incorporated into a FL, though. It would have to be heat exchanger tubes surrounding the outer drum.