If the Caps sign Ribeiro would they take Shattenkirk + Tarasenko for Backstrom? Doesn't Kuznetsov arrive after the Olympics in the middle of this coming season?
No. It doesn't address any of the Capitals' needs and sets them back in an area they've struggled to address for years (scoring center depth). The Caps are loaded with wingers and right-handed defensemen (especially of the puck moving variety).
Pushing John Carlson down to the third pairing and getting Kuznetsov's buddy is not worth losing Nicklas Backstrom. And honestly, Shattenkirk isn't even a lock to push Carlson to the third pairing.
And Kuznetsov has primarily played wing in the KHL.