I use a HC for free motion thread play when you want/have to be perfectly accurate with your stitches! Great idea Steve!
How about starting at an easier point and designing a HC for some of our non Singer machines that are impossible to fit a Singer/Chinese HC on even if they have a motor boss? I have a beautiful 1910 New Home that I'd love to get a HC for, but the only HC's available are for Singers! It is virtually impossible to find a HC for any machine, except a Singer, unless you get lucky and can find a vintage HC that was made for your machine.