Route concerns are needed only when you want to DRY your routes. So far you have only one route duplication (eoi) so... using a concern is an overkill here.
What you actually want to do is to have 2 eoi controllers, one will be responsible for providing all eois, second only for that ones which are inside the project.
For better readability I'd namespace them – put one eois_controller.rb inside projects folder and named it as Projects::EoisController, second one - as a top-level controller, named EoisController. Routes would look like this:
resources :eois # will map to EoisController
resources :projects do
scope module: :projects do
resouces :eois # will map to Projects::EoisController
end
end
And, of course, you might want to DRY these 2 controllers afterwards.
