It's a great looking bike. He has great fabrication skills. Better than I could ever dream of.
I do think it would look better without the funky black covers on the front and rear wheels. That might just be me.
Also to me it's just a show bike and would never be a practical rider.
First the front suspension looks like it has maybe 3 inches of travel, the rear 6+. Plus the wheel base has been stretched. Could make for some interesting handling issues.
Second the motor is a integral part of the frame. Yamaha built the 650 with a cradle frame. Early ones had problems. Cracks at the rear upper motor mount in the engine cases was not unheard of. It was also possible to break the frame. (My XS2 did both.) When they went to the 447 engine they beefed up the cases and frame.
He is using the engine cases as a stressed member of the frame. Not sure how that would hold up under real world riding conditions.