Will the cylinder even close with a rimmed cartridge in it?
The author tried and yes, the cylinder will close and lock. I'd guess he'd might have actually shot some rounds but with liability issues and S&W having tell him "NO", he didn't say in the article.
The author assumed it had to do with bullet size which was wrong and he should have known that. And he shouldn't have just let S&W tell him, no, but he should have gotten the real reason from them.
Now the .350L despite being called straight wall, has a little taper, like many semi-auto rounds, to aid in insertion and extraction. So the back of the chamber is about 0.01" bigger than it would be for a .357mag or max. This might bulge the cases, or split them, OR it just might fire form them.