The idea of adding ballast to the fastest cars will not work for several reasons. First, as Imari pointed out, there is no way to check the weight/ballast on individual cars. Secondly, let's say you add ballast to a car. Then the PP will go down and you can add Aero instead and you will get back the performance you lost by adding weight.
Tyre modeling also seems to be different. As Imari stated, the heat up much faster. I think you will have the most grip already at the second lap and go down from there. At the second lap, I think you also have a little more grip than you ever had before so best lap times will go doen a bit. This is good for our super lap qualifying. They seem to wear quicker as well. When I spun it seemed to used a lot of tire. I like this change too.