There's already an effort to do this using Scheme, it's just not ready for this release.
Is CL really that much better than Scheme?
Not from a language-theoretic standpoint.
From a pragmatic standpoint, all standard-conforming Common Lisp code runs on a conformant implementation. Schemes often tend to diverge (and they have 6 different Rn standards). So I think CL is 'better' than Scheme, for that value of better.
That way authors could transition from elisp to common lisp.