There are a lot of different issues related to the current functioning of register to read more and show unauthorised, and I think we need to try to solve them for 3.0. In some cases there are real bugs (like the redirect after logging in one) but on other cases there are some structural decisions that have to be made.
Basically, register to read more as a relatively simple concept before we had real ACL but now it is much more complex and complex to manage.
So here is my first proposal.
Part 1: Let's stop showing the "register to read more" string to users who are logged in. If we want, we can make a third string (in addition to "read more" for content you have access to and "register to read more" for content you need to login to see). But I think it's important to stop showing nonsensical text. So I would propose that we show that text only to the guest group.
Part 2 proposes that we let site admins configure which viewing access levels show unauthorised should apply to.
In the current system there is absolutely no guarantee that registering to read more will allow you to read more. When we just had 3 fixed access levels we could say just apply this to content with registered as the access level. But those days are gone. We have absolutely no idea what people will or will not be able to see once they register and login. If there is a registered level it may have a totally different name and number. I would propose that where we have the global setting for show unauthorised we add a parameter to limit its application to specific access level(s). By default I would set this to the default access levels that are associated with the default group that new users are assigned to (already a configuration setting). This would insure that registering to read more will actually let you read more.
There's more complexity after that, but let's start with that.
Elin