Those that overstayed their visa did not have to leave the country (avoid the lawyer that tells you otherwise, my family went through almost a dozen and several mentioned they had to leave, if they took that action they would have been banned for 10 years).

The change that you are referring to is for consideration for a waiver for the 3-10 year ban, where you would have to prove that you had to be in this country, and usually would involve a US Citizen that would be dependent on your stay. This change does not change anything other than allows you to have the waiver in your hand as you go through the adjustment process, whereas, before, you would have to leave the country and apply while abroad, if you did not get the waiver you where out of luck and had to stay.

People with credible cases would not follow through with this action because if it did not work it meant they would be separated, and immigration has not been the best with cases that are sensitive.