Detroit was in an interesting position last year - rebuilding team in the playoff hunt all season but knew that they might not make the playoffs or wouldn't make any noise if they made it, so they sold high on a guy having a career year just entering his prime.
I'm going to look for similar players to that in a similar team state. Some of the teams I could see in a similar position by the TDL are:
Washington (31 points in 25 games)
Detroit (32 in 27)
Montreal (27 in 28)
Buffalo (27 in 29)
Nashville (30 in 28)
Arizona (28 in 27)
St. Louis (27 in 27)
Minnesota (24 in 26)
Calgary (25 in 28)
Off chance of Edmonton (25 in 25)
From these teams, they have the following younger-prime aged defensemen that *could* be sold for a very high return ala Hronek.
Washington - Fehervary
Detroit - Walman, Seider
Montreal - Guhle
Buffalo - Jokiharju/Samuelsson
Nashville - Fabbro, Carrier
Arizona - Durzi, Moser
None from St. Louis
Minnesota - Faber
Calgary - Andersson
Edmonton - Bouchard
Of the above, the only players I see as untouchable are Seider, Guhle and Faber, and I think Calgary wants to build around Andersson barring a major offer. Samuelsson has been really good with Dahlin in the past and is locked up long-term so I don't see that happening either. However, there are three players that stick out that could be dealt in a very similar manner that Hronek was: Durzi, Walman and... Evan Bouchard.
Durzi has been a revelation for the Coyotes this season, and has shown much improvement on both sides of the ice. However he's still prone to big mistakes and is due for a new contract. Arizona has some very talented young defenders coming in and they seem very interested in Noah Hanifin, who would likely take away from Durzi's role on the team. Does that make him slightly redundant?
Welcome back here Detroit! Jake Walman has been a really good fit with Mo Seider and I expect they'll do what they can to keep him after his contract is done next season. Though, they do have some really talented young players looking to make a push and Yzerman has proven he likes to sell high on guys he doesn't see a long-term fit for. Does he expect Edvinsson to take his spot? If so, selling on Walman could be a sneaky good idea.
I'm torn on Bouchard. He's been incredible this season and there's been some talk about receiving Norris votes, and rightfully so. Even defensively he's been solid, especially under Knoblauch, which the mainstream fans/media don't like pointing out. He has a really good $3.9 Million cap too, but it expires after next year. Do the Oilers think he's going to be a perennial Norris contender worth the cash he'll demand? Can they look past his occasional brain-fart giveaways or losing his man in tight? Do they want two defenders making $9+ Million? I don't even think Holland has the authority anymore to make moves like this, but it's fun to think about
Any of the others could be moved and I wouldn't be terribly surprised, but these are the three I could compare to Hronek's situation the best.
Cheers!