Actually, I think this depends on the host. I think that as the night progresses the host can "mix it up" a bit with certain set piece songs... either for their comedy value, or as group montages.
I actually get requests from my regulars to sings certain songs that mean something to them, or ones they would like to hear. For a goof, I'll do "the streak" , and get one of my regulars to do the reporter... Always gets a HUGE laugh and thunderous applause.
"Boondocks", by little big town. I get two of my lady regulars to help out with that song... always gets a great reaction... especially when we go acapella at the end.
Of course, once the rotation gets long, I'll bow out and just run the show, and goof off with the singers. I don't think that's something you can define... you have to "feel it" a bit based on what's happening.
I always close the show with "goodnight sweetheart" and thank everybody for coming out... and I get folks wanting to to "do it with me"... and while I may start off (with 1 or 2 singers ), I usually hand the microphone off to someone in the crowd and let it run out... Its a lot of fun when a bunch of folks come up (especially the non-singers) to dance "sha na na" style to the song... its a great finish to the evening for those who stayed.
The key is participation... even from the "non-singers"... but this is the way I do things... and it works very well for me... other KJ's may not find this appealing. Conversely, I couldn't NOT do it this way... it just seems so natural
I don't think of karaoke as a bunch of people getting together to sing... I think of it as a bunch of people getting together to actively enjoy music.