They're safe with $450 (maybe even $500) assuming the following:
1. Microsoft doesn't undercut them by $100+ (If they do, Sony may lose USA by a small to potentially moderate margin, but still dominate worldwide)
2. Good launch window exclusive lineup (Horizon 2, Gran Turismo 7)
3. Profitable or close to profitable right off the bat
4. Developer friendly (PS3 was a nightmare early on)
5. A fair bit (50%) more powerful than the hypothetical Xbox 4
6. Launches simultaneously with Xbox 4 (PS3 launched a year late)
7. Backwards compatibility, with 4K patching for PS4's best sellers.