Ever since they've been a thing people have criticized their easier schedules. I think I'd be hard for them to get in even if undefeated unless all other prospects have one or two losses.
As for BYU getting in as an Indy I think it can happen, but it's take a long time (as in, hopefully by then we're in a P5). But, with our schedules getting stronger, BYU going undefeated would definitely get some press as a playoff contender. It would be tough but not impossible. The real problem is going undefeated.
I think the real threat to BYU is if P5 consolidates to P4. BYU likely doesn't make it in to that club as an Indy - we'd need to either be in a P5 conference that becomes a P4 conference, or get poached from one of the P5 conferences that goes away (ie B12)