The jury's out here but tending towards no. There's the concerns above and you'd still be on the road at either end getting to and from the on / off ramps with ground level vehicles feeling an even greater sense of entitlement & 'get orf moy laaaaand' attitude towards us. Especially those that couldn't or wouldn't pay or for whatever reason don't or can't climb 30+ fairly steep or spiralling feet up (its got to be, for economic & space saving) to reach the rooftop lanes. The off points would need a significant segregated reintegration zone or you're going to have a lot of gravity pushing you straight into pedestrians or onto roads, not good either way - or hefty and annoying chicaines on the off ramps that would likely scupper recumbents and trikes. Are they going to have dedicated teams of police and paramedics to protect and help users conveniently hidden away from the general view up there & at the on/off points? They would need to be laned and strictly enforced so the occasional Boris bikers and happy pootlers aren't in conflict with the strava set or crashing into similar coming the other way.