I seriously doubt slacking is the issue. The good ole boy system is the problem. The criteria for being an official doesn't have much to do with how good you are. There are some really really amazing high school and D2 officials who are much better at officiating than a lot of P4 officials who are flat out told "don't bother applying" because they're too tall or they don't have any connections or they're older than 50 years old etc...
It's your appearance and who you know. It's not a meritocracy. They bring in the good ole boys and/or people who fit the physical appearance they're looking for, and as long as they're not so bad that the national media goes after them, they don't care how good they are at officiating.
You see crews who make disastrous decisions trot right back out the next week unless it's so bad that ESPN anchors are calling them out.
So making it a full time job wouldn't help, in my opinion. The problem is at the top and the lack of concern that conference leaders have in making sure the officiating is as good as possible. If they had try outs and hired based solely on merit (they don't), things would be much better.