Exactly right. Nobody is doing it because there's not enough of a market.  The large percentage of guys running these aren't looking to keep a machine with those hours no matter how good the engine is.  Deere isn't going to help with the development and they're sure not going to work on it.  You're looking at a potential market of dozens...  Better start an engineering firm and get to work making that easy money.  Oh, and you're going to have to travel to the machines and do the conversions because there's a lot easier money for local shops to work on than combine engine swaps.