This presumes the player is riding the horse and using a weapon [specifically the spear/lance that formed the basis of that thread], but this would seem applicable to being 'bumped' an equine, although knockback might be the primary effect rather than damage.
[This would not be realistic (ya know, like the rest of MC ) as equines will kick and bite, but do not intentionally trample anything large. (The behavior seems to be linked to protecting the legs as speed is typically the primary defence.) ]
Given the stated rational for not adding sharks, adding even partially realistic hazards to dealing with feral (ie untamed) 'neutral'/'passive' mobs seems logical….
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.