output shaft viable repair ???

[Fazerider]

It seems overly complicated to me, but I guess it’d work.
Rather than weld through holes in the sleeve, why not just weld around the end? Better yet, as already suggested, forget the sleeve and build the shaft back up with weld.
If I was going to the trouble of rethreading the shaft I’d choose a more sensible pitch, the Yamaha one is simply too fine for the torque required. If you have a lathe available then cutting a suitable recess into the nut wouldn’t be much trouble.