I am tottally at the same page with LovinLauren. I would like to see Rachel "growing up"; also Sark in a different role; jen should be a guest star; aslo some Jack and Irina stuff. Even though a lot of Lena Olin's fans think that the intresting character wanished in season five, it truely dind't, at least in my opinion. All the years before she always had one hidden agenda... and in the end she was willing to give up everything, even her own family, for the goal she had been working all these years. Alias' final character was so cleary black - all the years before she had been between black and white. Writers wanted to show a different kind of Derevko... And there are even some speculations that Irina wasn't turely the real Derevko in the final season... And also, people change. Sloane understood after "helping Nadia die" that the main goal in his life was Rambaldi and anyone can't stop him reaching the final destination... at least that was what he thought.
I think that a spinn-off is very very very unlikely and also it wount be as good as it was during the "Alias" days.