This has been mentioned a few times before, and is considered for each generation of MineOS. Here is the previous one : The next version of MineOS.
There are several things here:
The first being that MineOS node is now in a feature freeze, since he has currently switched focus to the next generation MineOS.
Secondly MineOS relies the OS’s user management system, and relies on MineOS users to have a minimum of linux knowledge. MineOS was made as a WebUI to manage minecraft servers, not the underlying OS. For OS management there are several WebUI’s out there that does that better, like Webmin, that actually comes bundled in most of the ISO’s, even though it is disabled by default (to have the base MineOS ISO installation have as small a footprint memory and resource wise as possible).
A user management panel is therefore not likely to happen for the current version of MineOS (MineOS node).