Support! I'd love to see the clubs and registries be more active consistently, so encouragement for people to join in would be awesome.

support 

Halter shows bring in more $$$ than discipline shows if your horse does well, so the payout incentive is already there to join registries. More XP would be nice though. 

And if by "more active" you mean the shows will run more often, I'm not sure this will solve the issue for all breeds. Some just aren't very popular and there may not be active players with enough eligible horses for a show to run for, say, Welsh Type B foals. For this there's another suggestion floating around to force halter shows to run regardless of participant numbers. 

If you mean you want more community participation, I think that's on the club owner to generate interest in their club. Though it would be really interesting if the game offered competitions, challenges or achievements with rewards that could only be attained by working together as a club and impossible for an individual player to earn. 

Sorry for the long post :)

Support, would love to see this be an option although many club ownwers aren't active so it might make it a bit hard for certain breeds to enter comps but any way BIG SUPPORT