I think this would gather more replies if:

  1. It is sent as a patch that can be applied to the Guile source tree.

(You wrote:

 > If the community likes this implementation, I would be happy to
 > apply/rebase my changes onto the official repo, and then we can go
 > from there!

but to determine whether I'm happy with it, it would be convenient if 
this were a proper patch.)
(I'm not actually reviewing Guile stuff at the moment, but I find it 
likely that some others might hold the same view.)

  2. It is split into two patches: a patch that only does the hygienic
     rewrite, and an additional patch that adds the new features.

     Then people who are interested in the patch for the hygiene but
     don't really grok (or are uninterested in, or don't have time for)
     the new features can ACK or NACK the first patch without having to
     worry about the second patch, and additionally it becomes easier to
     verify there are no new bugs.

  3. You respect the LGPLv3.0.  The LGPLv3.0 requires you to follow
     most terms of the GPLv3.0, but you didn't follow 5(a),
     4(a) ‘keep intact all notices’ and 4(a) ‘give all recipients a copy
     of this License’ -- the LPGLv3 is more than only the LICENSE file
     you included; it includes parts of the GPLv3 by reference.

     Also, you only put the LGPLv3.0 text, without specifying a version
     number. Then by ‘6. Revised Versions of this License’ of the LGPL:

 > If the Library as you received it does not specify a version number of
 > the GNU Lesser General Public License, you may choose any version of
 > the GNU Lesser General Public License ever published by the Free
 > Software Foundation.

     you are licensing your implementation as LGPLv2.0+, but
     that's illegal, because your implementation is a rewrite of Guile's
     and hence most likely a derivative work of Guile 3.0, and
     Guile 3.0 is LGPLv3+ licensed, not LGPLv2+.

Best regards,
Maxime.