They really should have small gyms with bookable time (just a exercise bicycle maybe)
I've done the Sydney/Europe route quite a few times. The break in Asia does help; just to have a one hour walk around. As does first class! (did it once)
DVT is gone now, but still dealing with the repercussions. I ended up getting Schamberg's disease as a side effect of Xarelto, so both of my legs look like they're covered in a rash. I have some vascular inefficiency issues in my left leg that become prominent if I sit for more than 30 minutes.
Good times /s
I've been on many transpacific flights where enough people do it at the same time and all the aisles are blocked.
Going higher (for less drag) is a problem because it's hard to keep the engines running in the thin air, and on top of that, high speed also makes it hard to keep them running.
Until we figure out a new engine design, 80% of the speed of sound is about the max.
Military engines get around this by consuming incredible amounts of fuel - not practical for commercial flights.
That's why we're still at 0.8-ish mach numbers -- you can build those planes big and comfortable for the people who buy the expensive tickets.
Really long-haul routes might be getting into the range where people would be willing to sacrifice some seating space/amenities for a much faster plane. But then you're into needing much greater range than the Concorde. And, while there are a few of these routes that are economically viable on today's aircraft, even EWR-SIN didn't ultimately work out for Singapore Airlines.
You just need a way to get you to 60000ft efficiently!