The Feds already did their job by making it legal for the states to allow it. Whether homebrewing is allowed in your state is considered a "states" issue and the Federal government does not have any jurisdiction on it.
Yeah, if your state has restrictive liquor laws, that's all on your state. The Feds can't make states allow homebrewing. The Feds have some power in the commerce clause to regulate businesses, for instance to prevent discrimination within a legal business operation (no "whites-only" restaurants.) Since homebrewing isn't commercial, I don't think it falls under commerce clause.
At one point in time, the commerce clause was interpreted pretty broadly. In the case you mention above concerning the whites-only restuarant (Katzenbach v. McClung), the Supreme Court basically said that if Congress can reasonably conclude that, taken in the aggregate, an activity will have a substantial effect on interstate commerce, then it is within Congress' power under the commerce clause to regulate that activity.
It's a stretch, but Congress could conceivably regulate homebrewing under that interpretation. However, the SC has limited the power of Congress under the commerce clause quite a bit since that case was decided.