TS2, the BE may just add that 9th fb only school for schedule balancing. So no Temple anymore. However, the number of potential and acceptable schools that would accept that arrangement would be small. Army and Navy would be available. However, Army's experience with something similar in C-USA did not turn out well. Navy, assuming they would play 8 BE teams plus Army and Air Force (for certain), plus probable Notre Dame leaves them no room to play other OOC opponents each year. Navy, seem also to be comfortable with being fb independent. Last year and so far this year, they are having good fb success.
It is not certain even Central Florida would switch to BE for fb only, though that gives them better BE access and their sister school, USF, is already in there.
Two or more teams sharing one conference member "slot" for fb is not going to hold; at least in the context of a "9" team membership, and the allowance for a sharer to contend for the conference championship.
Obviously, the perfect solution for the BE is for ND just to agree to BE football. Since that is not going to happen unless there is a total surprise, the next best thing would be adding another "all sports" member or someone like Villanova moving up. Neither of those options seem realistic at this time either.
The bb expansion compromise in the NBE limited their immediate fb options. I expect the BE will wait on adding any more fb, and accept the 4-3 arrangement for awhile.