The ULR rest rules which SIA use on these flights give the crew considerably better rest than is achieved on normal long haul sectors by all accounts. I addition, as someone pointed out, they have lots of time off since they get to the flight time limitation quite quickly and they also receive extra pay for flying over 16 hour sectors. I guess it's horses for course but the guys who are doing it seemed to be quite happy.
As regards SLF getting bored on such long flights, anyone who has experienced SIA's IFE will be able to dismiss that idea: it's awesome with over 400 choices and individual video on demand and laptop power points in every seat. Now my last trip on BA longhaul was boring. How old is that IFE system?