I think @pf_moore’s argument is relevant: if you see these notices for dependencies of the things you want, that will pressure package maintainers to replace deprecated dependencies, even if they are otherwise perfectly happy to continue using them. Is such pressure desirable? I’m inclined to agree with Paul that it’s not.
People certainly might want to identify any deprecated projects in their dependency tree, and there should be a way for them to do so. But I’m not sure that showing that information on every installation is a net gain. Especially because projects can be abandoned without being marked deprecated, so you can’t assume something without this deprecation flag is safe or reliable.
I actually find that wording rather silly. You use any open source package at your own risk, and the popular open source licenses are careful to say so (in block caps!). And you shouldn’t expect that any open source author will give you support, unless you have arranged a support contract with them.
I know what they’re getting at, and that’s useful information. But I think it would be clearer to say something like “This package is unlikely to get any further development or releases”.