The barn where I board (which has 75 horses... everything from mini ponies to quarter horses to warmbloods to drafts) uses a custom made alfalfa-based senior feed that uses oil as a binder instead of molasses. Almost all of the horses are on it do fine.
I don't have my horse on it, however, because he's an easy keeper and if I put him on enough grain to get sufficient nutrients, he probably get very overweight. He also had ulcers when I got him, and so I try to keep him on an ulcer-preventative diet- having a grain-free diet is a big part of that. (I feed my horse Triple Crown 30% supplement)
IMO, ration balancers would make a great basis for a barn diet. Easy keepers get just the RB, and then horses that need more calories can get rice bran, beet pulp, and/or alfalfa added. Either way, every horse is covered as far as minerals, vitamins, etc, and gets the advantage of having low- or no-grain diets.