Apple could release it for other platforms (let’s not talk about the original Windows release). Or others could build a browser on the engine.
You’re right most people couldn’t switch tomorrow. Right now Firefox is the only credible non-Chromium browser I’m aware of for Windows/Linux.
Honestly that comment was mostly there to try to forestall the people I expected would come out of the woodwork with vehement Apple hate. And if someone did in one of the replies below my comment.