Facebook requires registering on Facebook. To many, including myself, it is a dealbreaker. I run a small IT company and I am plenty aware of the pitfalls of joining Facebook.
However, to address your issues. What is so 'last decade' about this mailing list that you think Facebook can do better?
You mention sharing media is a 'near impossibility'. What type of filesharing you would want? All I have seen are uploads of pdf files and photographs.
Most of the important information I have seen pass through here is messages/text.
Do you want something else? something like Pianoworld?
There are plenty of 'off-the-shelf' programs that can easily replace this Yahoo group without going to Facebook.
IMHO,
Bill