Think this trade works for both teams, even though Malkin is my favorite player and I'd hate to see him leave. Nashville has a plethora of defensemen, but have been searching for that #1 Center for years. Geno would immediately provide that, as well as chemistry with Neal on their first line. Pens get a 2C to replace Malkin in Colin Wilson, and get a Top 2 Defender in Josi, as well as move up in the draft.
Nashville would have to include more than just a 2nd. A 1st and 2nd combo would be fair.
You're severely undervaluing Josi. He's playing like a top 10 defensmen this year and is locked up to a great contract for another 5 years. Nashville doesn't do this deal if we try to pry a 1st from them.