Well, I come from the perspective of having a level of knowledge and familiarity with website management in general to make me "dangerous"...I learn as needed, but I if I were to "live on the edge" and something started acting wacky, I can easily get lost, and I don't have the time for that.
If I was knee deep in it at a level where I was partially "employed" so to speak (i.e. making money running a server, supporting sites for others, etc) then yes I would push the envelope. But for me, it's better to leave that to others, which will certainly do that.
I wasn't suggesting that no one should run anything beyond php7. It's just that for me, it's best to keep the potential problems at a minimum.