A point that I found in most aspects of R/C. You can try to make as many classes as you want, but people WILL make it expensive for you. There will be a special plane, special engine, special radio gear, etc. etc. Sad, but happens.
For this class, I think that the maximum engine size would have to be something around 46-50. This means that the planes would be smaller, and expensive gear won't make as big a difference. Also, it'll be cheaper, as I noticed that 60 is around the size where things start to get expensive.
Just my 4Cents!
Robert.