It's always funny when a few things go bad for a school or schools all these ideas come out.
Certainly a creative idea, but will not happen for a myriad of reasons, most described in post #2 with age groups changing each year.
The structure is clearly based on this year alone. Two years ago BGS would have struggled in the third tier. Last year GT came 4th in GPS and historically, as in last 4-5 years, have had the wood on BGS, BBC, TGS, IGS, heck even ACGS have probably lost as many as the won to GT over last 6 years. So if we started this for the 2010 season BGS and BBC would have to be in div 2 with GT in 1, or for 2011 ACGS, BBC, IGS would all be in division 2 before GT. There is too much variability.
Then if you look at the AIC schools, there is definite improvement and the NC/Marist games of late 90s were some rippers, but realistically when was the last time an AIC team beat a GPS team? Example using GPS easybeats GT. Marist haven't beat GT since 1993, not winning any of the past four games since 2006.