To a realm it had never been in before, I meant.
About your idea that Wickard turned Shreveport upsidedown, I’d like to clarify your confusion derives from the inappropriate inclusion of the registered carrier red herring and the mistaken attribution of “incidental effect.” Varying rates interstate lines was not some bug the perfectly constitutional interstate price regulation scheme accidentally stepped on. It was a major hurdle the feds had to jump over or blow through to achieve their dream of getting the railroads under their thumbs and stopping “predatory pricing.”
But like I asked: who said they could do that? In order to they had to exercise undelegated power. That it was necessary for the scheme is obvious, but not so that it or the scheme as a whole is proper. Hence their falling back on the intrastate price being substantially related to the interstate price. Which you say is because they were registered interstate carriers. But no matter, because intrastate commerce is not interstate commerce, even if done by registered interstate carriers.
You miss the forest for the trees focusing on the registered carrier thing. Why Wickard did not turn Shreveport on its head, and why it merely extended it a bit is that just like substantially affecting interstate commerce does not constitute being interstate commerce, being substantially related to interstate commerce is not to be interstate commerce. No matter whether you’re a registered carrier or not.
You might like to, but that doesn't mean you get to. You're going to have to do better than simply declaring it so.