I've asked many danseurs over the years, and have found only one solution that seems to work: wearing an outside belt with the tights, or even with a unitard.

I use belts that range from thin material to wide, some elastic, some very fixed and not too stretchable (like leather).  I usually wear a belt by first pulling my tights up, then placing the belt, and then drawing the tights up as far as they will comfortably go, then fold the tights back over the belt and tuck the material under the belt or sometimes roll the belt over.  

The belt is best positioned at the top of the dancebelt, but can vary a bit.  This seems to be the only solution I have found (and other dancers have told me) that works to prevent the dancebelt from rolling.

Wearing a belt outside over a unitard works, and can be stylish, too!  I have several different color belts (actually acquired from a sporting goods store; they're the belts worn by the baseball players with their uniforms) that contrast the unitard color.  They also give a focal spot to the unitard....I have a "long body" that looks better with this break in between.

You also said: "Also the manufacturers of dancebelts should consider a dancebelt leotard that can be worn under tights that do two things: absolutely no waistband roll over and the needed support. (No I'm not talking about male thong leotards)"

I have several leotards made out of a strong elastic material that provide support and eliminate the need for a dancebelt.  The material is pretty heavy, though.  Two have short leg bottoms, like boxer briefs, and I used to wear these leotards for summer classes. (They're pretty old, though, and I can no longer make out the name of the manufacturer.)

Play with the outside belt idea.  I think you'll find that it will be functional and can make an attractive accessory to your dancewear.

BalletMaster