after playing the guitar for 20yrs the 7 string was like a breathe of fresh air, it was new, yet the same. It really inspired me to sit down and start doing some serious practicing again.
I don't think the total capabilities of the 7 string have been entirely explored yet. I use mine for everything from jazz to blues to rock to classical, I've even worked out some slap bass lines on it just to p*** the bass players off.
A big plus w/the 7 string is you don't have to use any drop D or Eb tunings, no need to bring 3 guitars to the gig anymore. The 7 string has even made some songs easier to play because it gives you more options where to play the lower notes. And the chord possibilities are endless, you now have the broad range of a piano. The wide neck also forces you to clean up your technique.
Wether there here to stay, I don't know, but I know I will never go back to playing 6 string.