On a similar note, there is a branch in the guile git repo that aims at compiling to JS. It does a pretty nifty compilation pass that constructs a kind of minimal CPS where all calls are tail calls, giving instant support for delimited continuations and very simple (yet not fantastically fast) tail calls even in hosts that doesnt support it (using a trampoline).
Meaning, hopefully, full guile in the browser.
Is there a Scheme targeting Webassembly yet?
There is a WIP unofficial project from developers at Google called Schism [1].