Sure, so it's not a breaking change at 11.1. Map Viewer Classic is still available and you can view related records in popups as you can in earlier versions. You can also still build web app builder applications against those maps (at least for another year or whatever).
The reason I phrased it the way I did is because ESRI keeps pumping up their new offerings (Map Viewer and Experience Builder), especially as incentives for upgrading to 11.1, as the New Map Viewer is now the default map tool (at least compared to 10.8.1 which I had previously been running).
I also told my users about all the cool stuff in the new map viewer, only to have to backtrack and say "but if your application happens to rely on this very basic and important function, you're S.O.L." So yeah you can upgrade without issue, it's just tough to swallow that ESRI calls the upgrades important modernization steps, when they have actual step-backs in available tools.