Not so fast.
Do we want (1) a tool for debugging actual roles-related problems or (2) a tool allowing administrators to run academic what-if scenarios? Both are valid use cases, but for me (1) is far more important.
Tim and I discussed this in: http://moodle.org/mod/forum/discuss.php?d=91993
If we want a tool for (2), we should consider incorporating the functionality of the Role debugger into core.
The Role Debugger can be used by any user, not just the administrator, and it gives the user a complete analysis of his own permissions, not just his role assignments. I gave an extended use case for it in
MDL-13228 ("Improve the transparency of Roles...").
Please do not misunderstand me: I have been using the User's roles report since March, and I find it very handy for getting a quick snapshot of a user's global role assignments.
I have helped dozens of users debug complex roles-related problems using the Roles debugger (see the use case "A roles expert helping a roles novice debug a roles-related problem"), usually in a single iteration. These were problems of the most difficult kind – self inflicted problems created by administrators who had fiddled with roles without understanding what they were doing. In some cases the administrators could not access the site administration block.
Anyway, this issue should be linked to