I think online horse showing or coaching can be a great tool that very few people as of yet are ready to give a try because on the surface it sounds like a great idea but when a person gets thinking about it there are too many things that we take for granted with live shows that we can not take for granted with online shows.
As NRHAReiner pointed out IPHDA has one of the longest lasting online horse show formats so far (there is a online dressage show that has been around as long).
The reason for this is that IPHDA designed a new event (Performance Horse Development) and a judging criteria specifically for fair showing online. The judging criteria also allows for fair eligibility rules making the competitions fair for every level of horse and rider. This allowed IPHDA to take the online format from just for fun to serious competitions where exhibitors can win cash and awards.
Many others have tried online showing formats for all events and they end up being just for fun and dying quickly. (Horse Show World comes to mind) If large awards are offered chances are they will also die quickly simply because there is no way to make most events fair with the online format because of the arena size and condition, course size, jump heights etc play to big a role in the judging and pretty soon people realize that and wont play because they know it isn't fair.
The one event that does quite well online besides PHD is dressage but even the judging criteria for dressage would have to be tweaked to make it really fair online. But then again dressage is not about winning and losing it is about learning and getting feed back. (or so I have been told by western dressage folks)
I understand that horseshow.com will be hosting WD shows online for the WDAA in the near future and if you offer awards like you are for your current line up I bet you have some good sized shows at first. Then time will tell if an event without any eligibility rules can offer such large awards for low level classes and keep the numbers up.
IPHDA is also offering WD classes this January but only fun schooling shows so with up to $400 offered in a class you should do well at first. I wish you luck and if it comes to be I will make sure the IPHDA exhibitors know about it.