hey there,
as an avid user of rollers - much preferring the more natural feel of not being fixed on a steady trainer - every indoor season increases my desire to get a smart one.
checking the market this year i happened to find another option which should work with every classic trainer:
http://www.electricbicycleworld.com/Falco-edrive/
but i assume using it on a trainer (compared to the free spinning stand they offer) would add some resistance which isn’t factored in within zwift and therefore this combo wouldn’t make sense - right?
Searching the webs i couldn’t find anything about anyone who actually used it with zwift or similar simulators, so i’d be curious what’s your take on this.
Probably this would need to pair the algorithms of a smart trainer with zPower - which i guess never has been considered as a desired option 
thanks, markus.