Yeah there's no way 1984 Bob Backlund is going to agree to turn heel even if you held him at gunpoint. The idea that Vince suggested it sounds like he was trying to pull one of his moves where he asks someone to do something he knows they will never agree to so he can paint them as unreasonable. I would gather Bob saw that BS coming a mile away and just noped out.
Also looking back, there really wasn't any other person that would be a better transitional champ than Sheik. The cartoony Iranian heel is the perfect launching point for Hulkamania, I suppose maybe Ivan would have worked too, but he wasn't as over the top as Sheiky and the Iran/US tension was more of a hot button at the time than the usual US/USSR deal.
Actually, I've always wondered if maybe giving Sheik a little longer with the title to build heat would have made the eventual Hulk win even bigger and maybe some of the markets that were initially rough to break into would have had an easier time, but obviously things worked out pretty well the way they did it.