The problem I see is there will never be the parts support for the 855 as for other mainstream transmissions. I applaud Jamie for what he's trying to do, it's a huge undertaking and it definitely addresses a hole in the market for Mopars. I would love to have a five speed and not have to fabricate a new tunnel and crossmember. But even if he sells thousands of transmissions, what happens 10 years from now when you need a rebuild or grenade a gear? Will the parts be available still?
I know for most people that's probably not a huge concern. Most of these cars are used on a limited basis, the car won't have a 100k miles put on it and the lifespan of the transmission will probably be longer than that of the owner. For me, I could put 100k on my car in under 10 years, and I could have my cars another 30 or 40 years. If I buy a T56, well, there aren't just thousands of those transmissions. There are hundreds of thousands, if not millions, of them out there. Even if replacement parts aren't made in abundance, I can find other T56's for parts. But realistically, with that many transmissions out in the world there will be aftermarket support from multiple vendors for years. With the 855 you've got Passon, and you're not going to find parts on eBay or craigslist.