It's pretty tough reading BK's comments and other stuff and seeing a way the defense is much better this year. We lost a LOT of talent. KVR, Sheldon Day, and Jaylon Smith are not chopped liver... and Okwara/Shumate were solid.
I think these five things need to happen for the defense to improve (ordered based on likelihood):
1. Defensive line plays stout against the run based on sheer size... Rochelle + Jones + Cage/Tillery + Jay Hayes is a big group of linemen that should hold up at point of attack. Don't worry about pass rush, get that by creating free blitzers.
2. Shaun Crawford is a revelation at nickel.
3. Drue Tranquill returns to 100% and stays healthy the whole year.
4. Nyles Morgan is so good at MLB that it compensates for losing Smith.
5. After three years of being terrible Max Redfield somehow becomes not-terrible.
If all five of those things don't happen, the team is probably going to suck because there is going to be a huge deficiency somewhere. The only caveats would be true freshman like Studstill or Daelin Hayes or somebody playing out of their mind.
I don't necessarily think the defense has to be much better. I think they have to be more consistent and if BVG is worth a darn, he can get them to be. My thesis is that the talent is there, its not proven, but that's what coaches are for. Before I address your specific points, I must say that. Sheldon Day, Okwara, and Shumate just had their best years of their respective careers, why couldn't we get that type of play from Rochelle, Trumbetti, Cage, Luke, Redfield etc. I really don't think its out of the realm of possibility that we get better play from a lot of these guys. Not only that, but its what we should expect. If that talent isn't producing, then we know why.
On the issues you mentioned.
1.) I expect this to be the case. All signs point to Cage being a guy that has taken his game to another level. Like you said, those are some stout players and I expect them to be better against the run.
2, I don't think that Crawford has to be a revelation for this to be a net positive and thus impacting the defense in a positive way. I also wouldn't say that its extreme to think he could have a breakout year. This is a high 4 star talent with exceptional athleticism and perfect for that spot. I believe it was Lou S at BGI, that said during Spring practice, he can't remember seeing a CB impact 7 on 7 as much as Crawford did. Usually 7 on 7 is pitch and catch for the offense.
3.) I agree, I think that's pretty vital as of right now, and doesn't seem likely if history tells us anthing. I'd say valid concern. However, how much of a concern, I don't know. Because, depending on how he's used, we do have some talent that can play different spots. I think Studstill could play some of that SS role that BVG likes. Maybe move JO and put in Bilal at SAM or Martini. There are more options with more athletes, a good DC can get that done.
4.) I don't think Morgan has to be all world for the LB group as a whole to be better. Reasons why. Jaylon Smith is a hell of a talent and one of the best I've seen play college football. However, he only had 18 TFL's and 4.5 sacks his sophomore and Junior seasons. For comparison sake, Manti Teo had 23 TFL's and 6 sacks those same years. So the general impact that Smith had on the defense, could be argued ,that it was less than Manti. Manti just wasn't playing next to a Schmidt, where there was so much clean up needed. I expect that won't be the case this year, as there won't be that weak link on the field. Morgan + Whoever > Smith + Schmidt. Keep in mind that there were LB's that had more productive years that Jaylon last season, but he was the best talent. Collectively, I could easily see more production from that group. Also, with as much as BVG takes risks with his MLB, this is a scheme that seems to be built for a guy like Morgan. Morgan will have plenty of chances to make those plays. It's very possible that Morgan actual has a larger impact than Smith, in those areas (TFL's/sacks). Not a better player but more of an impact, because he'll be given more chances. In fact, my entire crux with BVG has been his lack of flexibility of putting his best talent in the right spots. Instead he runs his scheme regardless of who is where. Well, this is certainly the time to run what he did in the past, because he'll have an MLB that can make those plays.
5.) Again, I take a somewhat optimistic view, but the expectation should be players get better, that's what college football, or football in general, is all about. I expect either a better Redfield or Studstill that is better than Redfield last year.
I think some of the language is a little extreme. Suck and huge are extremes. For example, why does Studstill have to have a huge year, in order for it to have a positive impact or to play better than Redfield. You've said it yourself, Redfield has been garbage, why would Studstill have to be "huge" in order to be an upgrade over Redfield, isn't there some middle ground that is reasonable?