Guile Emacs was the work of one (very talented) guy. He's moved on to other things, but it's not inconceivable that another Guile fan will pick up the torch some day.

If enough Guile/Emacs fans get together this might actually turn in to a viable, maintainable project... this is, after all, how Neovim started. Just some people who were unsatisfied with where Vim itself was going, and teamed up to make their alternate vision a reality -- with great success.

Guile Emacs work is actually a much smaller task than Neovim, as Neovim's authors rewrote Vim from scratch, whereas Guile Emacs has a much more humble aim of simply allowing eLisp to be hosted on the Guile VM.

It could still happen.

The problem with integrating it is that you need someone with good knowledge about guile (since the elisp implementation is pretty bad currently) but even more important: someone who know Emacs internals (not many).