In the "invoke" branch of Kawa I've implemented more of srfi-140.
Specifically, I implemented substring (with sharing), as well as
list->string, string, and string-append.  All of these by default
return immutable strings, but return mutable string if you specify
--r7rs (or --r5rs or --r6rs) on the command-line, or import (scheme base).

This should be enough to catch compatibility problems.
I.e. if you have a Scheme code-base, it would be helpful if you could try
running it using (this branch of) Kawa, and note what if anything breaks.

If you want to try it, get the Kawa sources, as described here:
https://www.gnu.org/software/kawa/Getting-Kawa.html
Then:
   $ git checkout invoke
and build Kawa as described here:
https://www.gnu.org/software/kawa/Source-distribution.html

The Kawa support for srfi-140 is still unfinished; I've initially concentrated
on handling the most important old/standard procedures.
--
	--Per Bothner
xxxxxx@bothner.com   http://per.bothner.com/