There is no way they could use an insert in that flue upstairs. There is no fireplace to put an insert into. In addition solid fuel burners can't be used in a bedroomI have made the decision to modify the fireplace to this.
You’re correct especially about resale and moving insert. The modifications I intend to do will give me and the next owner the option of utilizing both flues. I will seal the left flue on the bottom giving the option of using it upstairs in master suit for a smaller insert and use right flue downstairs for current insert. Opening will be about 33”x 41”