That causes problems, by giving people power who aren't really qualified to have it. It pisses people off
What powers would trial mods get that they wouldn't have until global mod?
& the point of getting new mods is to take the load off of the other mods, so an approval system for all the trial mods actions would just give the current mods even more work.
At that point, might as well just not promote anyone and just have everyone use the report system.
It'd be a bit of extra work placed on the current mods, but with the goal of bringing new, qualified mods that will eventually be better off for the community (its only a week or 2 of babysitting a trial mod, for a "lifetime" of having a new mod). Im sure if this was the case, you'd hear A LOT less complaining about power abuse on this site