This makes sense to me, he's better than their best sprinter, and would back up Van Marcke really well, with a very strong team riding for the two of them. Also an excellent team to drive the peloton so fast over lumpy stages that even kristoff and degenkolb struggle.
Really hard to vote for a team that looks like it's folding though.
The thing Sagan lacks most is strong support riders in a reduced peloton - other than De Marchi, and possibly Moser/Formolo in future. He also misses a good leadout guy in the final km, where Cannondale is almost always absent.
For a future team, any ego clashing and joint leadership with his rivals in his targeted races (Classics leaders and big name sprinters) is out: eg. Trek, OPQS, Giant, Lotto, Orica, Katusha.
Doubt Sagan will want to be part of a team with a major GC contender, and hence much less support for him in stage races, even though in the Classics he would get great support: eg. Sky, Saxo, Astana, Movistar.
Best teams to fit the bill imo would be a revamped and stronger Cannondale, especially with the strong guys coming through the ranks. Also, BMC if Gilbert targets different races to Sagan, because of the support he'd get in GVA and so the 2 of them can fight for the 2nd place