From what I've read, personal API keys (issued to anyone) will continue to work fine, but apps that expose a way to use arbitrary keys (like in a settings UI, rather than hard-coded at build time) will be deemed in violation of ToS, specifically so that personal keys can't easily be used by the masses as a workaround for apps that have a 1:many dev:user ratio.

If you can build an app (or clone what someone else has built) that contains your key, you can proceed. This is fairly high friction for mobile apps, like building/patching an .apk and side loading it.