rfc0010: clarify scope of the proposed changes

Signed-off-by: Filipe Laíns <lains@riseup.net>

rfcs/0010-adopt-pep517-tooling.rst

-=============================================
-Adopt PEP 517 tooling for all Python packages
-=============================================
+=========================================
+Adopt PEP 517 tooling for Python packages
+=========================================
 
 - Date proposed: 2022-02-19
 - RFC MR: https://gitlab.archlinux.org/archlinux/rfcs/-/merge_requests/0010
@@ -9,7 +9,7 @@ Summary
 -------
 
 Replace setup.py with PEP 517 tooling (python-build/python-installer) for all
-Python packages.
+Python packages where this approach is viable.
 
 Motivation
 ----------
@@ -52,6 +52,10 @@ with
 
 You can find more information in the `Python packaging guidelines`_.
 
+This would naturally only serve as a general guideline, packages that need an
+alternative approach can still do so, but are recommended to stay as close as the
+guidelines as reasonably possible.
+
 Drawbacks
 ---------