Did this go anywhere in the end?
I hacked something together for my own use:
https://github.com/jamii/exo/blob/master/Emacs.jl
https://github.com/jamii/exo/blob/master/init.el#L180-L361
It can handle scoped eval, autocomplete and docs like Juno does (the addition of Base.include_callbacks in Julia 0.7 makes this way easier), but the emphasis is very much on the word ‘hacked’ 
The julia-repl emacs package works pretty well but it doesn’t have a backchannel to reply to the editor for autocomplete etc. Same for ESS. LanguageServer.jl doesn’t seem to support eval and as far as I can tell the autocomplete doesn’t take into account the local scope. Same for IJulia.
I would prefer to use a standard backend if one has been agreed on. Not so much a standard network protocol, but maybe a CodeTools 2.0 that contains tricky things like how to correctly redefine a module which may or may not be a root module, or how to figure out what module is in scope at a particular point in a file. REPL would be a good place for these, even.
I’ll start by making a PR this weekend for REPLCompletions that allows setting the module and returns structured completions instead of bare strings. I’d appreciate feedback on where to go from there. Also if anyone would care to review/sanity-check my module loading code that would be a great comfort - https://github.com/jamii/exo/blob/master/Emacs.jl#L35-L92