I think the national average will be around 70-75% just because recently commanders have done a lot more cutting themselves when it comes to cadets. In the past commanders didn't have to worry about cutting cadets or anything because almost everyone was selected for field training, but now they do a lot more of it. Here at my detachment we lost 17 cadets over the winter break and a lot of those were because our commander told cadets they didn't have much of a chance at field training. I'm sure it's the same at some other detachments too.
All of these numbers I see like 20% or 30% selection rate are just ridiculous. There are probably around 2600-2800 cadets nationwide competing for EAs. I may be a little off, but I think that's a good guess. Just because there's one less max doesn't mean things are going to change a whole lot either. I don't know if there's actually any information out there on whether or not they are going to make max 1-5 slightly larger, but I'd believe they would at least make them slightly larger.
This of course is all speculation from me, but I've always paid attention to the stats and how everything worked out in the past. I just think people will be surprised at how high the selection rate is going to be.