Access to closed projects

We use Intervals to manage our website development projects - each new website gets a project, and when it goes live the project gets closed and a new 'maintenance' project is opened to keep track of any small bugs / features that popup.

Occasionally, someone will raise something in the maintenance project and say 'I never asked for it to be done this way', but we can't check that as we've deactivated the project. We're on top shelf, so project limits aren't a problem, but we still want to close projects once they are done so people can't add comments and/or time to a project that has already been billed (we'd also end up with far too many open projects).

I'd like for there to be a new project status, "Read Only". They would show at the bottom of the list in the filters and look a bit different, you wouldn't be able to change anything, but other than that they would just be like normal projects. You'd obviously need to consider billing (free, part of normal project quota or separate quota), but I'm sure you could work something out.