I think this is worth a try. I've had HRCH's, MH, and many MHR's. I like NAHRA third best after hunting and training, but HRC and AKC/HTs are comparable games, my 4th and 5th choices. (I can't run much of anything with my wife's current health.)
An HRCH ready for a Grand only needs to spend a week or so learning to trail; the dog will likely have less trouble than its handler. A MH ready for one of their Nationals, needs to spend a little time on upland and the trail. Two NAHRA passes would show that they've done those extras. I think those handlers would also be amazed at how useful trailing can be in real hunting. Their dogs can do it, but learning a que will put them right to work in the field or marsh. (I have clear memories of a trail one of my dogs ran duck hunting when a crippled duck got up on an island opposite us and took off running. Well, that was a blind to a trail.) Having handlers and judges learn how to set up test trails is the only real challenge.
The different dogs will have slightly different strengths and weaknesses, but so would a group of MHRs to some extent. Many of them are already HRCHs or MHs. I think it would be fun to see good dogs from all three games run well designed tests set at the top of the NAHRA Standard. An event with under 100 dogs could be much more fun to run than the enormous national HTs.
All the games can learn from each other and this would be a great way for handlers with dogs at the top of their game to learn about The Original!
A double blind? Meah. I'd be more concerned about judges who could set up excellent tests, marks, blinds, upland and trail. Tests at the top of The Standard with good help, good grounds, good birds. Handlers would just have to be careful about the hangovers in a multiple day event ;-).