Going faster is one of the big advancements, but probably not the biggest.
Going 2x faster is obviously a good thing, everything else being equal. Costs can potentially go down as you can run 2x the flights per day. People enjoy flights more. The difference between a 2.5 hour and 5 hours flight is a lot. A 6 hour and 12 hour flight, a lot.
Making flights cheaper is something people consistently prefer. The main flight costs are fuel, pilots, staff, and airport capacity. Electric flights are interesting for short hauls but are a long way away from long haul use (much further away than supersonic). Automating away pilots is something that technically is easier than driverless cars, but hasn't seemed to be a priority yet. Progress there would be helpful. Removing staff on planes is a legal requirement and seems harder to do for larger flights for human reasons. Airport capacity is probably best helped by increasing turn time.
Honestly, the easiest way to improve the flight experience is to (effectively) get rid of all security on flights. Once planes can't be made into missiles (door locks were a good post 9-11 change), they are no higher risk than many other enclosed spaces that have no security. This would help speed of travel AND cost, and really means "just do less". But it's a political issue.
