IMO, unless done by a non-profit for a limited engagement, I do not think G&S can succeed at the box office today. Again IMO, G&S is seriously dated, unless you happen to like operetta; I doubt that there is much of an audience for it.
Have to admit that I have hated every production of G&S that I have ever seen. Even the 1980 production in which I had great seats. I find myself smiling for about 15 minutes, then I realize that I am bored, then I realize that I am very bored, then I can't wait to leave. To me, they are just too precious for modern audience tastes.
So, why was the 1980 production a hit? Well, first of all, it had a stellar cast (Linda Ronstadt was huge at the time, Kevin Kline was getting increasing recognition, etc.), it was well produced, well staged and choreographed, well performed, and the critics loved it. The only thing wrong with it was most of the G&S songs and the overall silliness, most of which wasn't actually funny, again IMO. I think I am a typical, pretty regular theatre-goer and, unless there was a monster cast, I cannot imagine purchasing tickets unless the cast was incredible, a even then I would probably pass. I know that many will disagree with me and cite the 2 year run. At today's prices, I don't see it.