I think the rumor you've heard probably has to do with the fact that anyone taking the test after June 5th will now have to spend considerable time studying for IR. So the logic would be that the person who took the test before the change would only have to study for AWA, Quant, and Verbal. The personal after the change will have to study for AWA, IR, Quant, and Verbal. So although the Quant and Verbal portion will not increase in difficulty, the test as a whole will be more challenging to study for, and therefore the test taking average out of 800 might decrease slightly.
I think this is definitely a possibility b/c people have limited time and resources. So when it comes to time, if you have to spend more time on IR and can't use that time on Quant or Verbal study, this will push scores down. We will only know how much the score will be pushed down after the test has been implemented. But especially for the first year or two, I could see the overall scores dropping slightly, but I don't think the impact will be great. Maybe a few points.
The other point you should consider is that schools are the ones that have pushed for a section like IR. So you want to do well in this section b/c it shows that you possess some skills that they are very interested in knowing about. So do you best... that's all you can do.
Not only prep time and resource constraints, but also ENERGY on G-day is a very BIG concern. IR (specially the MSR) will consume much more energy than any AWA.
IR will certainly stimulate our brain faster and prepared for Quant BUT seriously exhust energy... Verbal and RC will be great great challenge !