I honestly don't think Jon's feelings would get hurt if someone asked him about his voice. He's brought up his vocal problems (between the lines, of course) a couple of times during the last few years - for example, in this BBC radio interview last year. Listen to what Jon says from here on:
https://youtu.be/qH45ZhVoVF8?t=5m25s
He's fully aware of it. If someone directly asked him about it, his answer would probably be something like this:
"Well... first of all, I'm out. I'm old. I'm tired. I mean, I'm f***ing nearing on 56, hahaha! Then, when I think about all the hassle that's been happening during the last four or five years, I can't really help it. It's... (ten seconds' break)... it's been really hard for me to take. It's moments like this when you just want to give yourself the finger and say "Look at this mess around you, f***er, you're hurt. But you're healing." And I'm trying to do so all the time. It probably won't be anytime soon, but I'll get there again. I just need time. Thanks for asking."
IMO, the example above looks/sounds pretty much like what I'd imagine JBJ to reply, with all the curse words, pauses and everything. I just wish somebody had the balls to ask him about it. Truth to be told, Backstagers definitely wouldn't be happy, and Jon himself would probably get a bit off-track for a while (as he wouldn't be expecting it), but I'm certain that he would at least give some kind of an answer to the question.