The OP defeats his own argument. LSP was a collaborative effort that benefited from a degree of coordination that only hierarchical organizations can provide, yet it still sucks ass.
OP blames FOSS for not providing an IDE protocol a decade earlier, but doesn't ask the rather obvious question of why language-specific tooling is not only still around, but as market-viable as ever. I'd argue it's because what LSP tries to do is just stupid to begin with, or at least exceptionally hard to get right. All of the best language tooling I've used is ad-hoc and tailored to the specific strengths of a single language. LSP makes the same mistake Microsoft made with UWP: trying to cram the same peg into every hole.
Meanwhile, Microsoft still develops their proprietary Intellisense stuff because it actually works. They competed with themselves and won.
(Minor edit: I forgot that MS alone didn't standardize LSP.)
> OP blames FOSS for not providing an IDE protocol a decade earlier
Everybody standardized on Eclipse plugins almost 2 decades earlier anyway. It got replaced because the standard sucked. The new one is better, but by how much is still a question.
Maybe I don't ask too much from LSP, but it has enabled autocomplete on arbitrary languages across two or three IDEs I have to use regularly, so it satisfied my goals in a way the previous solutions did not.
I elaborated a bit when I edited my post, but to be more specific, I think LSP is a protocol that fails at its stated goals. Every server is buggy as hell and has its own quirks and behaviors, so editors that implement LSP have to add workarounds for every server, which renders the point of LSP moot. It's the worst of both worlds: editors are still duplicating effort, but with fewer, if any of the benefits of tools tailor-made for a specific editor-language combination. And that's not even touching on the protocol's severe performance issues.
Unsurprisingly, the vast majority of servers work much better with VSCode than other editors. Whether this was a deliberate attempt by Microsoft to EEE their own product, or simply a convenient result of their own incompetence, is ambiguous.
LSP is underspecified for sure. I don't think this is a situation that is limited to LSP though. It happens when software interfaces are underspecified (or post-hoc specified) with a strong dependence on a reference implementation (VSCode in this case) and the absence of a canonical validation test suite.
Exactly the same thing happened with VST audio plugins. Initially Cubase was the reference host, later Ableton Live became the reference and it was impossible to convince plugin developers that they were out of spec because "it works in Ableton".
My impression, having programmed against both the LSP and VST specifications is that defining well-specified interfaces without holes in them is not a common skill. Or perhaps such a spec (maybe ISO C is an example) is too expensive to develop and maintain.
OP blames FOSS for not providing an IDE protocol a decade earlier, but doesn't ask the rather obvious question of why language-specific tooling is not only still around, but as market-viable as ever. I'd argue it's because what LSP tries to do is just stupid to begin with, or at least exceptionally hard to get right. All of the best language tooling I've used is ad-hoc and tailored to the specific strengths of a single language. LSP makes the same mistake Microsoft made with UWP: trying to cram the same peg into every hole.
Meanwhile, Microsoft still develops their proprietary Intellisense stuff because it actually works. They competed with themselves and won.
(Minor edit: I forgot that MS alone didn't standardize LSP.)