I think any player on the team should be available outside of Lafreniere, Cuylle, Schneider, and Trocheck. I think Chytil has to stay because he won't have any real value due to concussions (unless you can dump his salary), and given his contract I can see keeping Kakko, but if some team really wanted him, I wouldn't let Kakko be a deal breaker. Kakko should be a solid 3rd line winger for a long time, just don't count on him to score 25 + goals and be a big scorer. If he is in the right spot in the lineup with the right expectations, he can be a value-add player at both ends of the rink.
As for Kreider, and every player on the team, I view it differently. I don't think the question is, is Kreider/any specific player the problem, I think the question should be is Kreider/any specific player the solution. I guess the way I am looking at things in general is this team is going nowhere. Everything should be on the table to try and move the team forward, including being bold and taking some risks. I believe that is the prism we should be viewing this team through now.
I also disagree that the Rangers don't have a lot of movable parts. They have to work around some limited NTC's and other clauses, but there is value. Dealing what is left on Lindgren's deal this season should be zero issue at all, the Rangers absolutely can get a pick for him. Even Trouba with only one year remaining is very movable, even if that one has to wait until after the season. The Rangers have players contenders would want for sure.