rfc: weaken claim about glibc future direction

I'm not sure about the political stances implied,
and regardless as the #1 glibc there is a huge amount
of software that isn't going to change between now and
any reasonably near future :).

rfcs/0023-musl-libc.md

@@ -86,6 +86,7 @@ The main arguments for inclusion are:
   higher-quality programs.  Recent versions of glibc have started taking stronger stances
   on enforcing compliance (look at patch fallout folllowing any glibc upgrade in last year or so)
   resulting in overlapping work from both sides.
+  (NOTE: use of glibc extensions or reliance on non-standard behavior is still common and unlikely to go away soon)
 
 And to a large extent:
 "Why not?" -- similar to including support for architectures such as Aarch64 or RISC-V,