If you extended the links to become chain stays, you'd get a stiffer rear end, providing bearings are right size and placed, and would obviously need full regig. Like the previously mentioned Katipo.
Zerode would be same weight and ride betterer, and with all the gearbox benefits. Although wife wouldn't maybe notice the flex rear, and may even be a bonus. Built in cornering suspension. I'm light and had a few different Brooklyns back in the day. Loved me to bit.
Looks fricken awesome, well done, very jealous. BMWs are still one of the best looking bikes ever IMO. Yours will look as cool probably.