I see what you mean, but we even have on the cards that soloists are welcome and we would jump in if they didn't want to stand there by themselves. This is also noted in our song list binders and I'm sure we'll be announcing it as well.
There are 3 on my staff so I plan on everything running smoothly. If someone turns in a card and that song has already been played, we will either let them play it (if it's been awhile and it's a slow night) or kindly ask them to choose something else. Everytime I have been to a karaoke night somewhere, there was no list of what had been played or what was coming up... It was up to the host to decide who was next and what songs were going to be performed and in what order. I think if it were more of a competitive gig, I would go with a running list.
The host will be congratulating and cheering on the departing band and calling up the next while the tech will be choosing the next song in the background while the slide show (and bg music) is playing. I do not expect (or want it to) it to last more than a minute or two between songs either.
I do like the idea of maybe having a separate list for those who don't necessarily want to specifically pick a song and other players, but would jump in at any time on their instrument of choice...just to be playing.
Great ideas everyone!