I am with you on this one and tempted to try the cross myself, interesting that you bring it up. The stallion many times does not pass the mechanics as most might think. The mare does matter a ton.
He is incredibly elastic and “slow legged” as the QH people call it, and we’ve found that our foals have always (and yes I say ALWAYS) taken after the mare in mechanics of movement. Our best moving mare has the best moving foal every year, and on down the line (worst moving mare = worst moving foal). I am sure someone will poo-poo me on this but we’ve found it every time. If mare is flat kneed, baby is flat kneed. If mare breaks at the fetlock, baby breaks at fetlock. Just watch a foal trot beside its mom and watch the mechanics. It may have slightly less knee, or slightly more, etc. but in general it is VERY similar. I am sure there are stallions out there VERY prepotent for adding knee (Sandro Hit, or what have you), or decreasing knee (Donatelli). Nothing is absolute.
To test this we had considered breeding one of our fabulous hunter moving mares to Quaterback to see if we could get that elasticity with the flat front end (if the semen wasn’t so darn expensive). The stallion does not have to move flat to produce flat. We had a Rosenthal foal last year (he does not move flat AT ALL) out of a flashy hunter mover which was a great, flat, elastic hunter mover. To me, it is the mare that matter more when considering movement. Novel idea, I know, but just watch some videos and really look. The stallion may improve the hind end, shoulder, etc, which increased elasticity and elevation, but the mechanics are mostly “mare” in our experience. I have never seen a 10 moving foal out of a crappy moving mare. I am sure it has happened but in that case you are breeding on “hope”.
If you want that big, lopey canter, and slow, reachy/swingy trot, you have to breed to something with tons of elasticity. That is what elasticity is! And yes, typically TB’s take away in this area.
It doesn’t matter what the stallion moves like himself but what he produces!
Look at the number of top hunters by Rubin Royal and then watch a video of him.
Westporte IS a stunning hunter mover. Watch a video of Wolkentanz, not near as flat.
Donatelli is a stunning hunter mover. Watch a video of Donnerhall.
Granted, neither Wolkentanz or Donnerhall have AS much action as Quaterback but I think it would be an interesting experiment. If you use a nice mare, worst case you end up with a beautiful dressage foal.