Personally, I do think Trumbetti, Tillery, and Jay Hayes will have big improvements this year, and that could be a big deal considering they do have 4-star potential.
On the other hand, that doesn't mean they are going to look like the 2012 team, where two out of 3 guys had 5 star potential.
But the biggest thing that was holding this D-line back lately (besides scheme) has been, IMO, the lack of consistent, confident leadership, like KLM provided (remember him "eating lunch" after big plays). They had big bodies, but not a lot of want-to (think Jones in the Miami game...).
Day was the last guy with exactly the right attitude. But it was cancelled out by bad leadership from the DC, and a bunch of young, inexperienced, subpar, or quiet teammates.
Tillery had his head elsewhere-- Showtime, Ireland, school elections, etc.
Jones was never fully healthy or bought in.
BVG, with all his antics, didn't have what it took to get their attention.
Jay Hayes needed consistency and direction.
BVG provided neither.
Trumbetti needed consistency and strength.
BVG and Longo were a terrible combo for that.
Rochelle was quiet.
Okwara was quiet.
Cage wasn't good enought to be a leader.
Add to all this a DC who refused to rotate meaningfully, and you have a really bad situation.
If there is any improvement in accountability and passion, which you are clearly seeing from Trumbetti, Tillery, D. Hayes, and even J. Hayes, there is going to be BIG improvement. The only issue is whether they can stay healthy enough to have good play at tackle, which is a real concern.
EDIT: Good to see Trumbetti and Tillery making everyone walk behind them on the way into the new locker room. Again, they look like they are starting to see themselves as alpha-males.