I agree with Charlie regarding keeping options open. If you really read McGill’s work in detail, his emphasis on side bridges, curl ups and the bird dog is within the context of minimizing spinal compression and shear forces in a clinical setting. His recommendations are conservative because they assume he is dealing with someone with pain or dysfunction. However, he also allows for the use of more stressful core exercises depending on the capabilities of the individual. Much of his book on performance training is devoted to evaluating who can withstand more stressful exercises.
McGill has stated in several places that there is a difference between training for optimal back/spine health and training for maximum performance, and the two goals might contradict each other at times. The key question is whether the individual can handle the training. As a practical matter, fit athletes are not going to have much trouble tolerating traditional ab exercises. Millions of athletes around the world have used old school traditional ab exercises for decades without causing back problems.
There really isn’t any reason why you can’t combine the static hold exercises used by McGill with more dynamic movements like the ones Charlie and others use. I think the static holds are nice warmups. And if you watch any of the videos of the ab exercises used by Charlie, a lot of them do not involve flexion or rotation of the lumbar spine, most require movement in the thoracic spine. Some do involve lumbar movement, but again, if the athlete can tolerate the motion, it shouldn’t be a problem. This is training, not rehab.
As far as making the side bridge more challenging, try this: from the side bridge position, rotate forward until you are essentially in a front plank position but only stay on one arm, do not put the other one down, then rotate back to the side position. This turns the plank into a dynamic exercise. Trust me, you’ll feel the ab muscles engage.