We've looked at LSIF before, and decided against it for a few reasons, mostly around COGS, operational overhead, and indexing latency. I gave a talk at last year's FOSDEM [1] going into some of the details. (Caveat that that talk was from when we were using a different open-source library, Semantic, to power fuzzy Code Nav. It's much easier to support new languages using the now-current tree-sitter query approach!)
[1] https://dcreager.net/talks/2020-fosdem/