They will give it something with a cool, marketable, and powerful sounding name. Numbers don't count unless it's a cool letter or number like 10, 7, X, Z, 8K, etc. The people who name these things have spent countless hours studying customer psychology so they want to give it a name that helps sell the product. They know that many customers know very, very little about the electronics they're buying and some people will buy into any bullshet reasoning for the name.
It's just like last year with the new Nvidia Turning RTX cards. People could not wrap their heads around the fact Nvidia called their new cards the 20-series but instead they thought the cards should be called the 11-series. Their reasoning is the 10-series was the predecessor and 11 comes after 10. The top of the line card of the 10-series was the GTX 1080 ti. Now, which name sounds more marketable, RTX 2080 ti or RTX 1180 ti? If you have a GTX 1080 or 1070 then why should you upgrade to the GTX/RTX 1180? Wouldn't RTX 2080 sound more convincing?
names are all about psychology!
I doubt they'd call it the XBox 2. Why? Barring refreshes, it's the 4th version of the XBox. Don't count on it being called the XBox 4 either because that would be like saying it's just as good as the PS4. They'll go with a name that stands out like XBox Edge, 8k, 5G, AC, XT, RX, Zen, etc.