Maybe I don't understand but there already is a dropdown menu that allows you to choose the format. The fact that the plugin is adding the arguments to youtube-dl that makes sure you get that selected format is why you don't always get the highest quality video.
While I know that works well when using youtube-dl interactively, that is not something the plugin can really do. It needs the url to get the list and that just makes the code weird.
This is actually an argument for leaving the plugin exactly how it is.
Ok, I thought about something like this:
1. I paste my link
2. youtube-dl checks what is available and opens the dropdown menu
3. I click the option I prefer (mp3, mp4, webm, mkv whatever) and the desired file is downloading
Yes, you are right, there is a dropdown menu. But I somehow couldn't take it for real since it was not working properly (if you know what I mean ).
And whatever format there is (mp4 or mkv) is fine for me.
Another question: Can you see how many people are using OMV's youtube-dl? If it's too much hassle to optimize a maybe not so often used feature leave it as it is (imho). I am fine using my other youtube-dl as before