My understanding is that the 4x AA size of battery rule was put in place to help make a level playing field as all good rules should.
Sure you could use all sorts of newer, lighter, more powerful and cleverer types of batteries but that is not the ideal for a class that is trying to promote itself as being easy and fun to build.
You would start to introduce cheque book racing which has seen the demise of many classes over preceeding years. Not desirable in my opinion.
The 4x AA rule is a good one…keep it.
My interpratation of the rule allows all types of batteries as long as they are of the international AA size?
in addtion to my last comment, I would have to add that if you were a Rookie sailing with, say, AA alkalines, you might be at a disadvantage to a more experienced sailor with, say AAA cells. So I would suggest that if you plan to sail a Footy with others, you have a set of AA and AAA cels ready to keep things even with the others.
To reiterate, despite the last paragraph of my last comment, I would vote for ‘stay with AA’. With the incredible amount of consumer products using AA cells I honestly cannot see them becoming scarce any time soon.