I think you will still be able to use your old gear but it won't be of the same level or tier as the new stuff. If Bungie had at least 1 smart person on their team they would solve these problems by offering an update or upgrade pack to the existing raids. That way we have new challenge and updated gear drops. Seems like a nobrainer because it works more for Bungie since this would effectively extend play time, minimize content creation, and keep players busy for months on end. Hell, I bet people would PAY for it.