Scholar possibly? That’s open to speculation (8)
I believe the answer is:
academic
This clue is a double definition.
'scholar possibly?' is the first definition.
(a scholar is an academic)
'open to speculation' is the second definition.
(academic can mean theoretical)
'that's' acts as a link.
(Other definitions for academic that I've seen before include "Of purely theoretical interest" , "Of theoretical interest, no practical application" , "Not expected to produce any practical result" , "Unimportant" , "Donnish" .)