Quoting RMS:
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Supporting Emacs extensions written in Scheme is part of the goal I had in mind when I proposed this. That's the tangible benefit that we would get from Scheme support. If all Scheme does is serve as a platform for Emacs Lisp, it is no real advance.
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See: https://lists.gnu.org/archive/html/emacs-devel/2014-09/msg00...
Hacking Emacs with Scheme is part of the plan.