Is there ANY practical difference between 70 lb med equipment with paws and 70 lb med equipment with hooves?

Except the provisions for mini horses are pretty specific.  One can easily say an miniature horse's presence will compromise legitimate safety requirements.

It is only emotional support animals that are affected by the change.  They will no longer be entitled to travel in the cabin, airlines can require that they go into the hold.  Service animals will continue to be allowed in the cabin including service horses although there are very few (they are hard to train because a horse startles easily).  If I had a service horse, I would request that it travel in the hold for its own comfort.

Some of your answers are idiots.

Mini horses are allowed to be SERVICE animals under ADA guidelines.   While they are not as commonly used as dogs, horses are used as guides for the blind and also for mobility support.

I reason that a horse would be better mobility support than a dog, since horses are built to bear weight, and dogs are NOT.

Horses also have significantly longer lifespans..  So a trained service pony will be in service for much longer than a dog will

I unfortunately do not know the reasoning as to why horses would be restricted for airlines..  Are they even allowed to be flown as cargo?    I know in situations where a service dog or other medical equipment is too large to ride under the seat or at the handlers feet, then it would be flown as cargo, and assistance would be provided to the disabled person.

Emotional support pets are not service animals.  

Yes, one is a dog and one is a horse.  That is one of the differences.  There is a big difference between emotional support animals and service animals.  If have NEVER seen a trained and certified service horse.