125M if Sony planned a relatively quick transition to next gen, 130M, even 135M, if Sony planned a slower one, with PS4 staying longer on the market as entry level console. Anything more is less likely, it would require not only a big price cut, but also a few new cross gen games and a decent schedule of older games budget versions, and probably a super slim restyling too, and all this done in time, as if the sales curve flattens at a level too low, lifting it again to viable numbers would require, if even possible, an excessive investment compared to possible profits.
So, to cut it short:
125M with little effort and no big mistakes
130M with some more efforts and no mistakes
135M with some more efforts and everything going the best way
More than 135M quite unlikely, requiring far more efforts, perfect timing and a lot of luck. Most probably not worth the investment, that money could be better spent to make a cheaper PS5 version possible earlier.