True, but I feel if many teams out there are looking to add Duchene, $6M in cap space, I don't see it unreasonable for teams wanting to add someone like Krejci who is in his prime. The problem though, as you mentioned, is his age.
I should have used the word suitors instead of market. In my opinion, I only thought there would be about 2-3 teams having any interest in Krejci, and when you factor in his NMC, the probability Krejci doesn't wave and finishes his current contract in Boston is very high. If the teams that missed out on Duchene are still looking for a top 6 center, there is a better chance Krejci waives his NMC based on the number of suitors.
I 100% agree with you about the return. Alone, I think Krejci returns a roster player due to cap reasons and futures. Something similar to the Kesler deal. In my opinion, the only way the Bruins can maximize Krejci's value to a team is to package a prospect(s) and pick(s) to get that comparable defenseman back in return if that is what they want to add.
This conversation is moot though if Krejci wants to stay in Boston.
I think the Bruins would have Bergeron and Backes as their 1-2 if Krejci were traded. Next year I think there is a good chance JFK could develop on the 3rd line at center and eventually replace Backes as the 2nd line center.