I'm interested in what performance is like for private packages outside of NPM registries, i.e using git+ssh... NPM is almost unusably slow to resolve these, yarn is a factor or two faster, and combined with it's behaviour of not re-resolving stuff in the package-lock this makes it just about usable for me - but even with yarn the overall experience of using many git+ssh repos is not great, it's even worse if dependencies are nested.
I'm not sure where the performance limitation lies with resolving git+ssh based revisions, but I'm pretty sure the existing package managers are not near the limit of what git remotes could provide - I've written some scripts relying on remote git tags with CLI plumbing commands and even that is not particularly slow.