Just curious: Why would someone do a TUI (text-based user interface) on a modern computer? Using C# implies that you're running on a device powerful enough for a traditional GUI. (And you really don't need much to run C#, just enough RAM / Disk for the framework and to handle the overhead of the garbage collector.)
Very common for server software, where you may not have a GUI environment installed. You can run SSH as a server on windows boxes easily now, and depending on your needs (or to standardize across a heterogeneous fleet of servers) it might make sense to have some good CLI/TUI utilities available that are cross-platform. While I imagine most people won't jump to a TUI for Windows, it could also be a secondary interface…
Then maybe a cool project is an adapter to allow the text-based GUI to work natively when running in a GUI!