I just wanted to +1 on this idea.
I am exploring this in order to get my text editor to nag about findings immediately without separate build steps. To implement something similar to e.g. linter-shellcheck[1] in my favorite editor it would help immensely if Lintian would accept simply the path to an existing 'debian/' directory as an argument, or even better if it would accept individual files (e.g. debian/control) and then run all the lints that are applicable to plain debian/* files.