My grandmother's friend had the two spool treadle. It worked fine. My grandmother would take me with her to visit and she would be sewing. I remember my grandmother saying it was a special machine because of the spool for the bobbin. It wouldn't be a big deal to make a canister to hold a spool of thread but a big design change would cost too much now for all the machine makers. Thread companies would love it. A new way to market and sell special thread spools.