Update roadmap to expand scope of declarative config goals.

docs/roadmap.txt

@@ -4,7 +4,9 @@ Roadmap
 
 Setuptools has the following large-scale goals on the roadmap:
 
-- Harmonize declarative config with pyproject.toml syntax.
+- Mature declarative config to supersede imperative config in
+  all supported use-cases and harmonize with pyproject.toml
+  syntax.
 - Deprecate and remove setup_requires and easy_install in
   favor of PEP 518 build requirements and pip install.
 - Adopt the Distutils package and stop monkeypatching stdlib.