using normal osroms and os files uae allows up to 8megs chip ram. thats were the os limit hits. its hardware right now that limits us to 2megs. if i remember correctly it is the chipset that limits it. so there isnt a hack to allow it. you would have to redesign the ecs or aga chips. the 4000 has a jumper on the mobo that would have allowed 4 i think (it does not work, so dont get your hopes up) commodore didnt put that into the aga chipset.
even if the aaa chipset had come out it probably wouldnt have been included since commodore built rtg capabilities into the os so they were probably thinking of moving away from the custom chipset