Arguably the DLR accomplished what it set out to do and it is very usable. I've used C#'s dynamic in a number of production project and even a deeper use of DLR constructs (IDynamicObject expression generation) in a few particular sets of circumstances. You can kind of see how Microsoft felt the DLR was "finished" because they solved a lot of the hard problems and made them seem simple and easy.

IronPython and IronRuby are still useful for doing .NET things in a REPL or scripting, though Roslyn's support for C# (and VB) REPL/scripting and F# have lessened the amount of time I spend with IronPython.

(I did recently hear IronPython rebooted and is trying to build out a full CPython 3.5+ compatible version, which was exciting to hear.)