Firstly, there probably is no such thing as 100% 'set in stone' but I feel the mark of a good team is when the team becomes increasingly stable with fewer changes and fewer players vying for positions. For example our Full Forward position is taken - Jack is our No 1 forward and the chances of him being pushed out by another developing forward next year is extrodinarily slim. On the other hand our ruck position is wide open with no one claiming it yet.
When we have very few positional unknowns across the ground we will be a great team but at the moment which positions are currently 'set in stone'?
Here's my view (in order) -
Tall Forwards: Riewoldt, Vickery, ???
Small Forwards: Nahas, ???,
Midfielders: Cotchin, Martin, Deledio, Foley, ???,
Ruck: ???
Small Defenders: Newman, Houli, ???
Tall Defenders: Rance, ???, ???
Interchange: ???, ???, ???, ???
So imho, by my calculations, there is only 10 definite lock ins. When we have 15+ we'll be regular finals contenders, 19+ and we'll be pushing for the flag.