What has been said about swimming pools and the like may not be too far off the mark if certain individuals have their way. There was a program on the tube last year where this group indicated that they were investigating using that future streached version of the A380 in much the same way as a cruise ship. In other words flying from airport to airport and having stopovers of suitable duration where the people live on the aircraft in the same way as they do with cruise ship travel. They were also talking of offering similar facilities. If that involved a pool then anything is possible but maybe that type of facility might only be available on the ground after a suitable preparation period.
Now this is probably only pie in the sky stuff at the moment but you never know.
Have a nice day