I really love C# but it seems like a poor fit for doing what you really want to do ("get more involved in machine learning, data analytics, scientific computing"). It seems like a detour and not a step toward your goal.
I would look on Indeed.com or some other job board for the jobs that fit what you think you would like to do and then look at the what languages and technologies they are asking for.
I've used C# for computer vision, visualization and even for embedded stuff but it really isn't popular for "fun" things and I think it will be even less so in the future.
At this point I am unsure if I should develop my C/C++ chops more or learn C# application development and add something new to the skillset.