There are a few issues with all of that though. 1) We have a lot of quality 4th line options outside of Engvall. Barabanov could be on the 4th line, in addition to Spezza (who could play center and wing) and Korshkov. In addition, there are over a dozen other guys who are great 4th line options on the open market, and most, if not all of them, bring a lot more outside of just defensive and PK ability. 2) Since PK is such a big part of his game, who is he replacing out of Marner, Kapanen, Mikheyev, Gauthier and Hyman on that PK? In terms of xGA/60, he is worse than Engvall and Mikheyev (and of course they do better in xGF/60 as well). Hyman is also better, but since he is a center, I am not going to compare the two. He is better than Kapanen and Marner, but not really enough to warrant bringing him in just to upgrade them on the PK. In fact, Kapanen is practically just as good, and near the top in the league in terms of xGF/60 on the PK.
Derek Grant, Tyler Pitlick and Kevin Rooney are three other UFA's who are likely going to be pretty cheap and were far better PKers than Nordstrom last year. Derek Grant is also an excellent FO center and brings a lot more to the table offensively. However in a weaker center market, he could probably get still get a deal in the 1.5 mill range. Pitlick is likely not getting a great deal, but he can bring more offensive ability than Nordstrom while still being a solid defensive/PK player. Rooney is effectively as good as Nordstrom, but had much better PK numbers on a worse team. Additionally, both Rooney and Grant had better xGF/60 numbers. Pitlick was slightly worse, but still would be a better option.
However if we are that concerned about our PK, we are just not going to trade Engvall. Engvall was the 3rd best PKer in the league (over 50 minutes of PK TOI) based on xGA/60 last year. Was also 11th in GF/60 on the PK (I originally said 3rd, but that was when it was a 5 on 4 PK). If you want a top 10 PK, you want more people like Engvall, not less.
EDIT: I did not see you mentioned Nosek. He would be a little bit better than Nordstrom for me, since he has a little bit more offensive ability and can take draws, but he was one of the worst PKers in the league last year (although his previous two years would make him slightly better than Kapanen) and still is not all that impressive to me. I would personally be looking at 4th liners who can bring more than Gauthier and Korshkov though, and personally, I do not think Nordstrom and Nosek really bring more than either of them.