Literally zero reason to keep an old console around if the next version of the console is backwards compatible.
If what I said above is true, then you have to think about this stuff as well:
- The previous console is X years old, and the likelihood of it dying gets higher the older it is.
- It's just going to sit there. Maybe on a shelf, maybe on a box, but it's still clutter to me.
- Could use the money I get from selling the console, and put it towards the new console (video games, accessories, etc.).