I think the transfer portal should be directly related to (1) coaching changes and (2) graduation.
If your coach leaves for another job or gets fired, you should get a free one-time transfer. This benefits the players, but also probably keeps schools from firing guys after a one or two year trial (especially schools that have no business paying millions for a buyout, then millions more for a new coach, when they aren't going to win any major trophies regardless). If you fire a guy, not only are you hoping the next guy offers a quality rebuild, but you're hoping he can fast track it by a year, because your roster is about to get pillaged by other schools. So some middling schools will ACTUALLY have to think about additional risks before making a move, which offers some stability for the players, but also gives a grace period to some potential up-and-coming coaches that might just need a year or two of extra seasoning to figure out the job.
Or, as previously/currently, you can move along without sitting out if you've graduated.
If you're just unhappy with your choice of college, or something comes up in your life that makes a transfer necessary, you can apply for a waiver... but the waiver should go through a committee NOT appointed by the NCAA, as their arbitrary, randomly-applied rulings were like 97% of the problem with the original transfer process anyway. The committee should be formed as a sort of "call up" committee to the playoff committee, that way it's made up of people with a legit interest in the sport, and they'll be motivated to pay their dues if they want to be involved with the playoff at any point.