I don't think long runs are a thing of the past. There will always be new things that catch on, be it at the level of Mormon or Hamilton or on the level of & Juliet or Matilda. We just shouldn't expect more than 3-5 of them per season to last more than a year. If anything, the middle-of-the-road "sleeper hit" may be a thing of the past. You're a juggernaut or you're dead.
The star-driven, limited-run play became more common around the time of the last financial crash, largely led by people like Scott Rudin, Jeffrey Richards, and the Roundabout. I don't expect that to go away anytime soon, but as discussed elsewhere, it's a lot to shoulder the burden of an entire play on one person (Leslie Odom Jr, Sean Hayes, Chastain, etc). The safer bet is a pair of stars, or an ensemble cast...but sometimes it's not the right combo of people (THE COTTAGE).