plover_michela VS plover-stenotype-extended

You can also try the Plover discord server, and go especially to the 'Italian' and 'theory development' tabs. I know I've seen people discussing the Michela machine on the theory development tab just recently, and there are other people working with the machine there who can help you. I think a lot of people are making their own keyboards as well. I have some other links for you to check out along those lines. The Michela machine channel, Michela Stenotype And The Universal Alphabet, and there are a few github and other such sites that will be useful here, here, here, here, here, and here.

See edited answer. But it’s quite flexible, and you bring your own keys. Example: https://github.com/benoit-pierre/plover_michela/blob/master/plover_michela/machine.py

There's an extension called plover-stenotype-extended, by default it comes with two extra keys but you could add as many extra keys as you wanted by modifying it. Adding the keys wouldn't be hard. The problem comes from adding all the new dictionary entries with the new letters.