What problem does this feature solve?

A lot of useful context is lost when invoking a 3rd party plugin after a project has been created. Like whether the project is using vue-router, or whether it's using dedicated files for the configs instead of package.json.

To check for many of these config options after the project has been created, you need to check if a file exists or not, or a line in a file, which is work that can be saved if the plugin developer can access what's in options param in the Generator API when the project is first created.

Another way to solve this could be to save that original context, like to a file, that then plugin developers can more easily read. The first way seems like a nicer experience for the Vue dev. Both solve the issue for the plugin dev.

What does the proposed API look like?

Imagine a new step in the vue-cli flow. It says...

Enter and any other plugins you want to install

And the user can type...

Enter and any other plugins you want to install
apollo, vuetify

Or maybe one on each line

Enter and any other plugins you want to install
apollo
vuetify