Actually, what if Pro (Slim?) was reduced to $299, with it's 8 cores, 4.2TF, but uses a 2.5" 1TB SSD instead of an HDD? Could they better compete with XBSS for a few years that way?
No, PS4 games are not developed around a SSD, you can just some load speeds and that's it.
The SSD of next gen is a vital part of game development from now on, last gen simply can't compete with it just having a SSD on it (which you can try on your PS4 and see how it works).