It would be helpful if FBIs were supported on ~object datatypes~ [Abstract datatypes] (edited).
Currently, that doesn’t seem to be possible:
create index lines_fbi_sdo_idx on lines (id, startpoint_sdo_geom(shape));
ORA-02327: cannot create index on expression with datatype ADT
02327. 00000 - "cannot create index on expression with datatype %s"
*Cause: An attempt was made to create an index on a non-indexable
expression.
*Action: Change the column datatype or do not create the index on an
expression whose datatype is one of VARRAY, nested table, object,
LOB, or REF.