As an aerial tanker i don't really see it has much of a future right now. Airhips are just too much of an easy target to be used anywhere near a danger zone. But as strategic transports they seem to create a niche that no other transport mean can compete with. Imagine a craft carrying 500-1000 ton payload anywhere in the world, without refuelling, able to land on unprepared ground, where even rugged airlift transports like hercules couldn't land. All that at some 120-150 km/h, and still far less fuel spent per ton per kilometer than a C5 could deliver. Once again though, usage will probably be only in areas completely uncontested by enemy. Actually i see first usage in commercial, civilian areas, before armies get on the bandwagon. Timeframe for all that? 20 years sounds reasonable.