Is it really possible to be active enough to be champ in 2 divisions?

After the main event last night, Islam is moving up to WW.
I just don't see how a fighter can effectively move up and down in weight (between two classes 15 lbs apart) and still defend twice a year each belt.

Do you think Islam should vacate his belt? For him having this insurance is great obviously, but I do not think it is good at all with all the inactivity... We would have more inactivity and more interim belts, which sucks.