Plunger-styled rear ends went the way of the Dodo for good reason ya know, Paul.
The rear axle was prone to hike at different levels/heights during their compression and thus not keeping the axle "true", or at least as true as the swing arm rear suspension which would supplant it.
(...I actually think the rear end on this concept looks pretty damn smart...I can't really see it all that well, but it looks like a take on the Harley softail design)
