Uber is not "Sharing Economy" (there are various lift sharing sites that are proper sharing economy sites - where driver is just sharing a lift & makes no profit (the important part!) - passenger cost just covers petrol / wear & tear (& so possible on normal insurance) , these tend to be more suited for regular commute journeys)
Uber should just be subject to same rules as other cab companies (so in UK, drivers & cars certified by local authority, have appropriate insurance)
Not convinced by the 5 minute rule. A minicab company I sometimes use is a minutes walk from a train station so, if I phoned from the station, they would be (driver availability permitting) be there in far less than 5 minutes & an enforced wait pointless so I simply walk to the office, order a cab & then get in it (I assume no 5 minute rule if booking "in person") - however that walking approach not good for someone with mobility issues who would have to phone & needlessly wait.