(self-promotion ahead)
Since the Microsoft Teams client is well known for being quite frankly, terrible, as many have pointed out in this thread, I am working on my own, alternative Teams client: OperCom.
I'm building it as a simple, vanilla JS web application, in a SaaS model (since I need to keep bending to Microsoft's will). The Teams API isn't great to reverse engineer, but it's do-able and has been done (partially) before, but never to the extent required to create a full-featured app.
If anybody's interested, you can see its current status at [1] and keep updated with its progress at [2].
[1] https://blog.opercom.co.uk/posts/news-13-08-22/ [2] https://www.opercom.co.uk/contact