Just another one of my ideas.
As I understand it, they had to drop the bikes from the original MvH race because of the legal aspect of cycle racing on or across bridleways.
Catton Park gets used for MTB, running and horse events, so how about a MvHvB race there ?
Eastnor Casle looks like another suitable venue to me too, and I'm sure there must be others around the country.
Could it work ?
Who could put it on ?
There's quite a bit of cross over between cycling and running, with some people either racing in both or doing duathlons, but there's not much connection between the athletics and horsey worlds, so it could take some organising.

I shall now prepare myself for the usual "It will never work" (it already has elsewhere) and "I don't want to do it, therefore nobody else should" replies.

I live a mile from Eastnor and have done for nearly 20 years, in all my time I've not see anything horse related at the site. Im not sure why.

But it sounds like an interesting idea. Not sure what Eastnor estates would have to say about a second biking event held there.

Surely the horse would wipe the floor with the other two?

Not always.
http://en.wikipedia.org/wiki/Man_versus_Horse_Marathon#Winners_of_the_race

it all depends on the course. I believe Tim Gould made a good showing back in the day at Llanwrtyd Wells.

Horses can be beaten if the downhills are fast and the climbs give them no real advantage!

If you look at the discussions before HoNC and HtN about whether a CX or MTB would be quicker on the course, I'm sure it would be possible to devise a course for runners, horses and cyclists that gives none of them a significant advantage.

They design the course carefully to handicap each group equally – or try to. Which is why it can be close.

To the OP – think what you are saying. Horses would seriously TRASH the trails!