There's always been progression in all of our racing events. How we deal with it often determines the success or failure of the particular event.
Example: A ton of effort was put into coming up with a set of "B" team race rules that (1) didn't obsolete everyone's airplane, and (2) that everyone could live with. The result didn't work out too well in the long run for many reasons. If I had to do it again, I'd be more stringent in the powerplant department.
As far as F2CN... under the current rules, It's been somewhat frustrating, yet fun at the same time. The biggest issue to me, and far bigger than airplane construction, and fueling issues etc., has been heat management in the engine. Trying to find settings that give some decent speed and lappage, yet keep the engine warm enough not to lose it on a pit stop glide, are certainly more difficult to obtain with an F2CN than with a fully cowled F2C model (at least for me). I don't know what the answer ultimately is, but I have a Nelson with steel P/L to try...
Bob, just a tongue in cheek response, now realized you were just kidding about opening it up to all 2.5 diesels.
Les