Microsoft is starting to port VS studio (IntelliSense) which is proprietary to VS code which is opensource.
Current C# plugin (Omnisharp) is opensource, so they announce that it will be replaced by a closed source selector that let you choose the opensource or the proprietary plugin with the proprietary as default.
It's Embrace, Extend, Extinguish just in front of our eyes, so opensource people are pissed.
Most of the heavy lifting in OmniSharp is done by Roslyn [0]. Roslyn is the open source C# compiler and code analysis library maintained by MS. You cannot overstate how much effort has gone into Roslyn, and how much money MS has invested to make it work. OmniSharp is essentially a wrapper[1] around Roslyn (before Roslyn it was Mono), and while the OmniSharp team did a nice job developing a nice intellisense UX around it all, it is not like MS is taking it all away from them. Incidentally, it is almost certain that new intellisense plugin by MS will also be built on top of Roslyn.
And all of Microsoft's proprietary extensions look for official proprietary VS Code and refuse to run on open-source builds lacking Microsoft's private key.
I'm still confused too. How exactly does this "LSP Tools Host" fit into the larger platform of tools? For example, how does it affect me as an Emacs user?
Now that .NET is easy to run on non-Windows platforms, Microsoft is likely trying to figure out what's the business case.
By keeping the tools to them, Microsoft can try to offer the best developer experience. Hopefully (from Microsoft point of view) this pushes developers to use services from their ecosystem (Github, Azure).
It's likely that in the future more developers are actually doing the development remotely. Not checking out the code to local machine, but instead using IDE which communicates with the server component. Microsoft has Github Code Spaces [1], JetBrains has Fleet[2]
