I don't see anything wrong with it.
It's just another one of those things where people who have never had any experience in doing something automatically think it's wrong without knowing much details about it. I see that all the time on animal forums and find it very puzzling. You'd think that people would be all for things like this that add some enrichment :?
Yes, you need to use your common sense. yes, don't try to force your rabbits to jump. yes, some rabbits are nervous and just want to hang out in their hutch/run, never want to leave the garden, and only want human interaction when it's treat time. But not all rabbits are like that. Some thrive off various kinds of enrichment, enjoy learning, enjoy jumping and don't mind harnesses. It's not really that hard to understand that rabbits all have different personalities and all enjoy different things and you should take that into consideration with each individual rabbit and treat them accordingly. You'd think a group of rabbit owners would know that. But every time something that's not widely done comes up (and I remember the jumping threads from several years ago, it was the same thing then too) people act like all rabbits are delicate little creatures that shouldn't be messed with, only observed. Apparently even tapping them might break them into a million little pieces.
Maybe I'm being a bit harsh here but, I don't know, I guess I feel like rabbits are really underestimated. Dedicated rabbit owners think they're super delicate and kinda treat them more like decoration in some ways rather than living creatures. And the general public thinks they're stupid and boring. And seeing things in black and white is generally not a good thing when it comes to animal care.
I also think people worry too much sometimes about what the general public thinks. If anything, it's got to have a positive effect on the general public because they'll see that rabbits are active and smart and they can't possibly run around and jump in a 3ft hutch. And really, who thinks the average person is going to put much effort into training their rabbit to jump. The average person can't even be bothered to teach their dog essential commands. Rabbits are being underestimated and people overestimated lol.