Of course in order to reject that healthcare qualifies under interstate commerce, they would need to either reject Wickard v. Filburn and Gonzalez v. Raich, or jump through some crazy hoops to justify upholding those, while stricking this law down. (Although I'd not be shocked if this court tried).
Actions regulating healthcare within one state have at least as much impact on interstate commerce as growing pot or wheat for personal use. Healthcare is not strictly limited to state lines. My insurance does cover visiting doctors in a neighboring state for example.
Reopening Filburn would raise a crazy amount of questions. USDOT regulation of commercial trucking could falter if Filburn was struck down. Until some new clear line on what the limit was, there would be widespread uncertainly about the federal government's ability to regulate things like commercial trucking, flights, drugs, etc, at least for transactions that don't cross state lines.
I doubt they would actually go that far, as the republican party are not actually anti-federalists, despite often pretending to be that way.
