Why would someone use Neptune instead of just using Jupyter? I see how Pluto has a new value proposition that Jupyter lacks (reactivity), but it looks to me like Neptune simply removes that value.
It's also an unmaintained fork. Forked in February and hasn't a commit since to the source. None of the patches are getting downstreamed. It just keeps updating its README and posting more advertising. If someone wants to do this project they should do it correctly, but this is just not how you do that. You'd need to keep floating your patches over a changing master, not just force an old version, force all packages to be on older versions without patches (HTTP.jl), etc.