It would be great to be able to give clients access to their project in build mode / as a user with the marketer role. The only way to do this at the moment is to add an extra seat to our agency plan for $35, which is way too expensive.

As an agency we have many client projects in our workspace. Many of them use the editor to make content changes. For each client who needs more functionality, we move their project to their own hosting account. This makes handling client projects more complicated for us. Giving them access as a user with a marketer role (at a reasonable price) would solve this.