Ok I've gotten the specifications for the battery not even sure how I found them but it's compatible with a 7.4v 2s lipo is what it says but doesn't tell me much else
In theory you could upgrade all of that to brushless and lipo. Gut all the electrics and add in after market parts. You may have to fabricate a motor mount but that can be done with some hobby plywood.
I would just go with a hobbypartz setup until you can piece the scorpion system together. I wouldn't put that kind if money into an affordable boat. Personally I would get the boat kit first then build the power system around that.
We'll see that's the thing I am getting a rockstar 48" nitro offshore catamaran in August and I plan on getting a lot more in to boats so I figure if I get a soiled system I can always drop it in another hull down the road but you maybe right with the scorpion to start.
Scorpion is a great setup. Down side is the investment needed to get it together. Also check out the for sale ads on the forums. You might luck out and find a great deal.