John, thanks so much for your analysis - I knew you'd nail it. I have a few more random thoughts.

Echoing what you said, I don't think it's possible for a band with the talent of GPN/AS to remain 'underground' for as long as GPN did anymore. We got years from GPN in which they built their following by PLAYING IN FRONT OF PEOPLE who almost always got 'converted'. These days the digital opportunities to get in front of people are so many and so varied it's more a problem of over supply than anything else. 

Still, there will be occasions when an unknown band blows away the right crowd at the right time. Did anything like that happen at SXSW this year? Well, maybe down on the genre level (see, for me, "Field Report") but no way on a large scale because everyone already knows everybody. 

<img src="http://static.someecards.com/someecards/usercards/b4c755c5b493b5da56c611ab67e940d468.png" />

Still, it's not hopeless for discovery. I can talk about three or four bands that I think are on that path to being very popular as long as they get themselves in front of as many people as possible (the GPN model). Most of these folks though would not appeal to the general public or, more importantly, to the 'tastemaker' crowd. 

If I stumble upon another GPN quality act I'll let you know - or maybe I'll start a blog . . .