I like Desktop and I use it at home. I think it has many strong points and some weak ones.
The fact that it’s not HTML + JS is a plus in terms of security and privacy. A lot harder to exploit.
I think it can be simplified, say for example drop protocols and concentrate on XMPP maybe SIP. Remove options, codecs and configurations not needed anymore, due to improvements on hardware, etc. As an example, just use x264, x265, vp8, vp9 and opus.
Another suggestions is to mavenize it.
The Remote Access and Control is almost good… a little modernization would probably go a long way.
Message History can be modernized using just the history stored at the XMPP server, there’s a XEP for this… (NPI)