It really depends on which way the management decides to deal with Kessel. It will be obvious to them by TDL (if it isn't already), that Kessel will always need a defensive anchor around him, and that anchor is likely to drag the offense of the line down (Bozak, Komarov, Winnik, Panik, etc).
If they decide to part ways with Kessel for a king's ransom, then anyone and everyone is fair game (minus Bernier, Rielly from the current roster). Lupul, Gardiner, Phaneuf, JVR, Bozak, Kadri and Komarov. Basically, anyone who you can get a reasonable return for (pref 1st rounders). Even in that circumstance, I think Franson could be a valuable character guy, well-spoken, by all indication wants to stay on his childhood's favorite team, and could be just the type of leader a young core of players acquired during a retool need.
In either case, I'd like to see him signed at around 5 x $5M, but would grudgingly accept 6 x $5.5M. In a few seasons, that'll be the going rate for 2nd pairing D, which is pretty much Franson at his absolute worst, with the whole PP specialist thing tossed in, as well.