To put it plainly, Sayu sucks at doing the kind of hip movements that requires a certain snap and power. She never really got better at that, see the Updated Manpower and the like

She is definitely selling the sexy though, just from her expressions alone hnghh
ughhh Fantasy ga Hajimaru ;___;
If they put it in the setlist that'd be like twisting the knife on what is to me the end of the Fantasy T_T
Her final solo song should by all rights be Aruiteru. It's the song that gave her the confidence to keep toiling away in MM when she was feeling the most under-appreciated and she said it herself that it's like her life's theme song. The lyrics would fit like nobody's business too...
Wouldn't mind a new song that sorta ties it up with all her usual trademark songs mentioned above though, including her duets with Fukuhime and Tokisora (I'll forever associate that song with Sayu from now on T__T ). If anyone can pull it off and do her justice it's Tsunku. But Aruiteru
must be there.