Following up on BobDigital's interesting post above, here's a "swing for the fences" far-fetched straw man.
1. I would plan on running a predominantly 4-2-5/2-4-5 sub defense using "interchangeable" EDGE rushers and penetrating DTs. There will still be some hybrid "base" sets, but sub is the new base. I want some jumbo wide bodies to stop the run against certain teams, but mostly I'm looking for penetrators, not 2-gappers. I want to scheme pressure from all directions.
2. On the back end I want to continue to play a physical press-man scheme, with a lot of complex coverages. The Pats have one of the 2 best single-high FSs in the NFL to guard the back end of the field and to play cover 3. He's wasted in cover 2 and as a zone CB. And I want a true "stud/star" DB who can function as a 3rd LB, stack the box, support the run, play in the slot against RBs/TEs/slot receivers and drop into zone coverage is an important piece.
3. Traditional MLBs aren't a focus in my defense. As I want to play mostly in sub, I will only have 2 true "LBs" on the field, both of whom need to be both MLBs and EDGE players. A coverage LB and LB/S hybrid are both important positions.
With this in mind, and with Jabaal Sheard already signed, I would do the following:
1. Trade Jerod Mayo and our 2015 1st round pick to Chicago for CB Kyle Fuller. Fuller isn't Revis, but he's younger and cheaper and very, very physical. I trust his character and work ethic far more than someone like Marcus Peters. Mayo is expendable, as I under-value true MLBs and he's not really an EDGE hybrid.
2. Re-sign Brandon Browner. With Fuller on board as a #1 CB, it makes sense to bring Browner back. Fuller and Browner would be the most physical CBs in the league.
3. Trade Alfonzo Dennard, Tavon Wilson and our 4th round pick from TB to New Orleans for Kenny Vaccaro. If the Saints can trade Jimmy Graham they can trade anyone. Vaquero fits perfectly as the stud/star hybrid.
4. Sign UFA DTs Nick Fairley (on a "prove it" deal) and Kenrick Ellis. Ellis will combine with Sealver Siliga to give 2 good "jumbo" run stuffing DTs. Fairley has some risk, but is a disruptive DT who can combine with Dominique Easley to help scheme pressure inside as well as out.
5. Sign UFA EDGE player Akeem Ayers. He shouldn't break the bank, and he's another versatile hybrid player.
6. Sign UFA LB Colin McCarthy. The Pats have already had McCarthy in for a visit. He's a solid MLB and coverage LB, and would be far cheaper than Jerod Mayo. MLBs aren't a high priority in my blueprint.
7. Draft DT/DE Marcus Hardison day 2, and LB Ben Heeney day 3, and possibly a DB to pipeline. We don't need a run-stuffing DT, an EDGE player, or a safety. Hardison, like Easley, is a versatile chess piece who can be used to scheme pressure on the DL, and who will excel in sub.
With that in mind, my defense would look something like this:
"Big" DT: Sealver Siliga, Kenrick Ellis. Big run stuffers have a role, but shouldn't break the bank.
Penetrating DT/DE hybrids: Nick Fairley, Dominique Easley, Marcus Hardison. Tons of disruption inside. Chris Jones is expendable, or can fight for Buchanan and Moore for a back end roster spot.
EDGE: Chandler Jones, Rob Ninkovich, Dont'a Hightower, Jamie Collins, Jabaal Sheard, Akeem Ayers. The strength of the team. Michael Buchanan, Zach Moore and Darius Fleming can fight for a possible roster spot.
Off-LOS LB: Colin McCarthy, Ben Heeney. Athletic, versatile, and low cost.
Star/Stud/SS: Kenny Vaccaro, Patrick Chung, Nate Ebner
FS: Devin McCourty, Duron Harmon (Logan Ryan)
CB: Kyle Fuller, Brandon Browner, Kyle Arrington, Malcolm Butler, Logan Ryan, rookie
I'd be pretty happy with that defense. My "money positions" are penetrating DT/DE hybrids, EDGE players, star/stud hybrid safeties, aggressive press-man CBs, and a great single high FS.
Realistically, I doubt the Pats could pry Kyle Fuller from Chicago. A trade up for Marcus Peters is more realistic. But as a straw-man, this is the closest thing I can think of to what I would do if I could.