I agree that if the weight limit is lifted, then it should apply to all AMA classes. However, the 2m rule will seriously restrict what you can do with open-ended weight rule. The wing loading will not be lighter enough unless it is a biplane. Then the question is whether it can fly as good as a regular pattern plane. People could start to optimize the big biplanes similar to the regular pattern planes, FG fuse etc. And the cost could go up.

If the 2m limit is further lifted, thena pattern becomes a different IMAC competition?

It seems to me a cost-effective, very competitive 2m and 5kg plane is all needed to draw more folks to pattern.