I have been playing around with the custom user levels and have been finding a few things missing. The big one is in our org there is a need to allow for users to be able to view sources and identity profiles as well as the configurations of both (read only rights). This would be read only access.
The question is, has anyone found a way to add permissions that are not in the UI to a custom level yet? If not I will need to make a trip to the ideas board.
If you find there are things you consider missing, you can provide that feedback in the feature announcement and the product manager should see it there and can respond. If others agree with you, they can also respond there as well.
Now, if your missing items are not actionable by them immediately (most likely), then you will need to make the trek to the ideas board. If you do, please link the idea to this topic so others can find it.
It sounds like you are desiring a FULL Read-Only Admin option, where the user can view ALL configuration pages as read only. If so, there may be an idea already for that.