it would take a flukey series of events to open the door. Even then, it's probably only BSU that would ever have a chance due to their current reputation. They would need to be undefeated and then they'd have to hope that there were no more than two other undefeated or 1 loss P5 teams. Could it happen? Yes, but unlikely. BYU, on the other hand, would have a much better chance to due some very real schedules in the future. I don't think it's opinion that BYU has better access to a national championship than any G5 team. In fact, it seems pretty self-evident.
The only way G5 teams have an advantage over BYU is for those seasons when BYU ranks somewhere in the 10-15 range, give or take a few ranking spots up or down. Any season where we're top 9 or better, and we're in a NY6 bowl (more or less - some years there are fewer at-large slots than other years). Any season where we're ranked 16 or lower, and chances are there's a higher ranked G5 team that would grab the G5 auto-bid anyway. So, G5 membership really only helps us grab a NY6 game under a pretty narrow set of circumstances. There is no way we will ever even entertain the thought of giving up the advantages of independence for a better shot at a NY6 game under that narrow set of circumstances, while at the same essentially locking ourselves out of playoff consideration. Why anyone would endorse a path that guarantees that BYU is a permanent member of the have-nots is hard to understand.