Just give the console a number. And. Increment.
That's it. You can still have Pro / Slim / whatever models, but I have no idea why Nintendo and Microsoft both willingly threw away the easiest marketing strategy there is: your kid has the 4 and the 5 just came out. 5 is larger than 4 therefore the kid knows what to ask, regardless of age. The parent also knows what to buy because 5 is larger than 4.
Nothing convinces me that this isn't the reason why new Playstation models sell like crazy before any decent games are out. 4 was larger than 3 and 5 is larger than 4. That's it.
Nintendo got out of it by starting a new line of consoles with the Switch, but Microsoft's marketing just keeps giving this one away to Sony for free. It's unbelievable.