I second your skepticism, his reasons for not signing here last year seemed pretty concrete: his family is rooted in Det, he is loyal to the city, and he's publicly stated he's not a ring chaser. Maybe he's changed his mind, but Det was a mess last year when he refused to sign elsewhere.
Sheed is no slouch at the same position, he's good for the game, he would bring his own unique skill set to the position, and he's great friends with Garnett. I know many here have taken his agent's 10mil comments to heart, but I can see him as a much more likely candidate to take a discount here. He'll win a ring, play with his friend (last time he did this he won a championship), and it would increase his value around the league for 1 final signing.
Just one man's opinion...