I know you're kinda joking (or maybe not) but I wonder when the day will come, where managers ARE loaned out?
Imagine, a young, promising manager, oh I dunno, let's give him some anonymity and call him BVA for argument's sake, isn't quite acclimatising to his new surroundings... who's to say he couldn't be loaned out to a managerless, mid-table, lower league side for a few months, (Portsmouth for example, I hear they're looking for someone) whilst the Good ship HTFC is steadied, ("Evening All") ...then he can learn his craft, potentially do well at that club, and... oh, it really won't work will it....?
Probably the reason why it's never been, nor ever will be tried!