Currently Mains gas is still the best option but that wasn't what you asked. Future proofing was the query.
As for gas conversion, I was around for the conversion from Towns gas to Natural Gas (just). It was a huge operation, whole streets turned off and disconnected from the system and access had to be gained to every single property in the land connected to the gas network. If they couldn't gain access you were left disconnected!
Anybody remember
wobbe numbers? Injectors were as rightly said all changed to alter the air gas ratio but also altered was combustion air requirements ( Natural gas required approx twice as much air to burn IIRC ) which again was a massive undertaking especially for open flued appliances.