I think that something that some of us are missing in Silverstripe is a preferences page where to change some user settings or global settings without the need of editing a config file. In my case this would include the preferred user language or the default site language, but some other settings could also be changed, such as the username or password or some class-statics. I've seen that Markus has implemented a custom form to change the password if you have lost it, but i'm not aware of a way to change it through the cms interface if you don't have access to the security administration section.
A possible option could be to add a main menu link to a Preferences page where this fields are displayed and can be changed. Each of this settings can have an associated required-permission. Classes could add new fields by registering them in some way, in order to be extensible and modular.
Another issue is where to store this preferences: the database option is perhaps the easier one but if we read/write dinamically _config.php we'd be able to modify this file to change things if we wanted it, same as now.
What are your thoughts on this?