[ralph84]

At this point there aren’t any trijet designs like that being built, and it’s unlikely we’ll ever see a new trijet design. It served a role in the transition from four engines to two, but now with ETOPS-370 there’s no commercially viable route that can’t be served with an appropriate twinjet.

[filleduchaos]

There are several passenger trijets still existing - they are just not commercial airliners. Dassault for one is quite fond of the design; the Falcon 900, 7X and 8X are trijets, and I'm pretty sure the latter two are still in production. I wouldn't be at all surprised to see another trijet design from them probably around 2030.

[Gare]

The Falcons have all three engines tail mounted, so not the same "type" of trijet as MD-11.

[secult]

Don't forget about Tupolev Tu-154. It didn't stop flying as a commercial airplane because of safety, rather because of noise emission limits.