Where's Kyzer! Maybe he could find time and one of the 'respect/time' scripts on Facepunch and throw in some extra code.
I personally don't see much want for this. I've seen 'regular' players on various servers I (currently, used) to attend regularly, and many of them just wouldn't make quality admins.
I like the message idea.
Perhaps have an option in the script to turn on/off notification on individual players?
I'd be willing to use it more then. With the option on, I'd have to type /blah_track <player> before I'd ever get a notice about them.
I could see that being handy.
Player: "But, you've seen me here everyday for two hours at least, JamminR! Can't I be a server <lowest member access>?"
/blah_check <player>
<player>:steamid has played on this server 20 minutes since <date>
Me: Uh, no.
Month later, they seem nice, no minge activities.
/blah_check <player
<player>:steamid has played on this server 4 days 3 hours 2 minutes since <date>
/blah_track <player>
<player>:steamid is being tracked. Once they reach some <optional time_till next level>, the access will change.