An absolute nightmare in economy in a B787 in 9 across configuration. Market limited to traffic between PER and LHR only as Asia and the Middle East offer better connections to other destinations and no one will suffer an 18 hour flight followed by a 2 hour lay over and then a 1 hour flight.
The last trip I did Asia to Europe I broke the journey for a few hours in the Middle East. Enjoyed a session in the gym, a few laps of the pool and 20 mins in the jacuzzi. After a nice meal in a restaurant I was quite happy to get back on board for another 7 hours. Stayed airside the whole time and as the flights were daytime was quite happy in economy.
Up to 4 hours, a low cost will do.
Up to 8 hours, economy in daytime on a decent airline.
Beyond 8 hours I'm looking at breaking the journey or business class.
A premium fare will need to be charged to cover the cost of the extra fuel used vs a stop in the desert. It might be better to go as far as Dubai and feed into the EK network.