I think everyone is tiring of the guest host gimmick - some faster than others
I'm bored of it. But i also have caution over a full time GM. If you get a good one then great but if you get a bad one then you are stuck with them.
What i'd propose if a 3 month GM role. Where they can use someone but they will only get a 3 month role and then change it. That way you can get better GM's in but if they are good they won't lose their appeal and if they are bad you can give them less on-air time knowing that a better GM is coming.