Most of the bands that play covers are either tribute bands, or play to a genre and/or period in time. Right now, '80s hair band covers are popular. If you want to stay ahead of the curve, you might try doing grunge. It's only a matter of time before that's the latest nostalgia music.
FYI I heard (from a TV in Chicago, over the phone) that Pearl Jam is playing at Wrigley Field
this summer. To make an exception to their self-imposed rule of "lite rock and Country only" for their nighttime concerts means that '90s music must be coming back. IJS