Personally, I'd look to implement QA sooner in the process. If developers are looking to design differently, this can affect QA, so having them be aware is important. It can make the entire process smoother.

However, I'd make sure QA knows that "informed != getting to design". Instead I'd look for someone in QA that can handle hearing about potential changes without getting worked up. If they are aware of what might be done, they can be thinking about the impact to QA. However, they do have to know that they can't begin changing their test process until the design is finalized.

Takes a very level headed, thoughtful person to do this.