Here's some interesting info on Horowitz' piano; focusing on the Mohr era Steinway.
https://www.ptg.org/pipermail/pianotech/1996-August/008929.htmlHere is an interview with Franz Mohr on his work with Steinway and Horowitz
https://www.dw-world.de/popups/popup_printcontent/0,,2105212,00.htmlAnd a list of Horowitz' pianos.
https://web.telia.com/~u85420275/trivia.htmBasically, Horowitz' super light action required lots of expensive hammer maintenance, and is therefore impractical.
The focus on what Mohr did to Horowitz' piano should be taken with a grain of salt, which if placed on the keys would no doubt produce an audible sound, anyway.... Mohr didn't start working on Horowitz' pianos until about 1965. Some of VH's most memorable recordings are from the 1940s. His dynamics, ranging from ppp gentle to mega crashing fff are evident on some of these recordings. I have a recording from Carnegie Hall of Kabelevsky's Sonata #2 that begins with absolutely thundering chords. Harold Schonberg has a very good biography of Horowitz and he talks a little about his pianos. In the biography he says that the '40s era piano was found in the Steinway basement. It was one of the first with Accelerated Action, and according to the book, this action was designed by Paderewski. Paderewski was a piano tinkerer, but someone else holds the patent, so I think this info is inaccurate. In any case, Horowitz' early piano piano was more or less "stock" rather than a custom redesign. Alot of articles on his piano suggest that the dynamics of his sound, especially the thundering bass chords, were due to the custom action. I think it was the performer rather than the instrument.
Also, the action that Horowitz used was removed from the piano before the "play Horowitz' piano" tours. I'd read variously that the action was thrown out, or is sitting in Franz Mohr's closet. Apparently Horowitz allowed only a very people play his piano, Murray Perahia being one, so there are very few people who could authentically say what it felt like. By the time he was using the piano with the Mohr modified action, Horowitz was rich enough to have his piano shipped all over the globe. So he didn't have to adjust for a piano with heavier action, which would be the case if most of us had our personal piano so modified.
Personally, I'd like to have one with really light action, though if I wanted to afford the hammer maintenance for such a piano I'd have to give up eating.
Joseph