As an avid Planet of the Apes enthusiast I agree with you about the horses because we need them but Dragon-Models puts out a decent one already which you can still get individually for about $35-$40. Sideshow’s US Cav. 6th Michigan Bugler and the CS Cav. 1st Virginia Cavalry look great on these.
It would most likely be more costly for SS to try and duplicate this great sculpt as well as having to make a multitude of saddle variants from McClellan, western to your general all purpose saddle. The next issue would then fall on designing all the different horse blanket schemes.
The few minor problems I find with Dragon-Models horse is that its neck position can not be adjusted and it only comes in one color. Making horses would be a great idea and very welcomed by probably most collectors. Image where you could go with this if SS made Native American Indians? *Insert whistle here.*