The biggest problem with player groupings is that this is a strategy that is employed by low talent teams to overcome the talent deficit. If every player executes every play perfectly, you can somewhat overcome a lack of talent.
The fact that the coaches couldn't execute the strategy was a problem.
But, the fact that D2 Danny thought it was an appropriate strategy to employ at a historically good D1 football school was a bigger problem, and further evidence that he was in way, way over his head. He had no idea how a big boy program should be run; the fact that he thought he could/should get there with tricks and shortcuts just ensured that the minor hole in which GB left the program became a major hole.
But, back to Shane. At this point, we're just seeing practice reports, and seeing him being given time practicing at a particular spot. We have no idea what the conversations are in the position meetings and/or individual player meetings. It could be that the coaches are already confident of his ability at tackle, and want to give him a lot reps at guard so he can play there too. It could be that they think his ceiling is higher at guard. It's probably that they want to put the best 5 guys out there they can, and Callahan is a much better guard than Irwin. It could be that they think Nembot will be better with Callahan beside him. There's a million things it could be, and 99% aren't "bad."