@Cmaier could speak to the challenges of switching from N3B to N3E far better than I ever could. From what admittedly little I understand, Apple uses big ass caches (using a highly technical term) and N3B has a 5% density advantage compared to N5, while N3E offers no change. The main benefit to switching to N3E is the cost sharing involved with other companies, because Apple is likely the only major customer for N3B. Also, TSMC may want to switch everyone over to N3E so that they don't have to worry about two parallel lines. Again, from what little I understand, doing such a switch isn't a trivial or inexpensive process.
I put this rumor in this thread because of the comedy of MacRumors quoting a Weibo source. After WWDC, we can see that Apple has succeeded in locking down the leakers. As you stated in your epic rant, Gurman was dead wrong about his predictions. It was only a few days before WWDC that he vaguely admitted that the Mac Studio would get an M2 update. He completely missed the Mac Pro, insisting it would be later this year. Kuo lost the plot a long time ago. Even Ross Young, who I don't think is a hokum peddler, has fallen flat with his iMac and new desktop mini-LED monitor predictions. Now that WWDC is over, we're back in silly season. Perhaps Apple will utilize N3E, I'm not an expert, I don't know, I just question whether some random dude on Weibo knows the truth.