Hi Sam,
As you have shown there is a place for a JetA1 piston aircraft. However I'd suggest regular London-Capetown-London trips are not done by your typical pilot. I would suggest for the average owner a JetA1 conversion would not make economic sense.
A turbo system failure will not result in total engine failure of an Avgas engine like it will on a JetA1 piston engine. There can be a variety of reasons for a turbo system failure, not just the turbo itself.
I haven't had the opportunity to fly an SMA engined aircraft. No doubt they are very good. I hope they're a lot better then the Thielerts were, 300 hour gearbox inspections and all, though I understand that inspection time has now been increased.