I think the number after PlayStation works perfectly for it. It sounds good. Looks good. And they're at no risk of a "WiiU" situation.
But the idea of something like "Nintendo 3" sounds a bit weird to me. Maybe I would get used to it, but I think they went in the right direction with how they name their systems. But it can be hit or miss.
For Xbox, I think the same numerical naming system PlayStation uses would suit it really well.
Xbox 1, Xbox 2, Xbox 3, Xbox 4, etc.
But I suppose that was never a good option for them, because PlayStation would always be one number higher than the Xbox. And even if you only lose out on one sale because of that, when a parent is looking at which console to buy for their kid, and picks PlayStation 3 over Xbox 2, it's probably not worth it.
As for the name of their next Xbox Series X, I'm not sure what to think.
But there's an emphasis on an X again. So it can look similar to Xbox One X.