The Wickard test is incredibly broad. Wickard was a case about a guy growing wheat to feed his family (no sale, interstate or otherwise). The basic ruling is that if the activity has an impact on interstate commerce (there, in the fact that he had an impact on the supply by not buying) then it's actionable under the Commerce Clause. Recent decisions have refined this to something "having a nexus with commerce" (the case that added this said that mere possession of a firearm on a school has no "commercial nexus" and thus isn't covered by the commerce power) *plus* the Wickard test. Home ownership comes about via a purchase, which generally is where you get these sorts of restrictive covenants stopping people from displaying the flag, or from condo associations, which are ongoing commercial relationships. So it's definitely got that "nexus" and as far as "impact," you get wildly long chains of causality (for instance, owning a home changes the available supply of housing in an area, impacting living expenses for others and thus encouraging or discouraging wage changes, immigration to your state, etc.). I'd prefer applying a proximate cause test for commerce, but hey, dems da breaks.