Very exciting! I’m not quite clear on where HLS stands - the blog seems to suggest that HLS already works, but then also needs a cabal repl with multiple home units support. Could someone clarify what’s needed to currently get the best experience?
A cabal release that gets the PR merged would be the first step 
From the Cabal side we’re very excited to have received this contribution!! And personally I know that this will greatly encourage people to draw boundaries between the component of their code if ghci/ghcid work seamlessly with it. At least at work this will allow us to restart the tests when the library code changes
I think the HLS PR for it is Add support for multi unit argument syntax by wz1000 · Pull Request #3462 · haskell/haskell-language-server · GitHub, which, once cabal multi-repl is merged, allows us to use HLS with cabal’s multi component support.
Looking forward to having ghcid restart on library dependency change! I’ve been using the flag hack, but that of course doesn’t scale across number of local packages.
cf. https://github.com/haskell/cabal/pull/8726#issuecomment-1472868209