I reckon it will be a lot more than 4GB. If Sony manage to get the 10 years or near 10 years out of this Gen, we won't be seeing the PS4 until maybe 2012 or thereabouts.
Seeing as the price of memory is getting cheaper and cheaper all the time, I reckon we will see a 8GB or even 16GB as you say 7th Gen console.
Although if MS release the 720 or what they will call it as I predict in 2 years time then I can't see it having more than 4GB.
Prediction (June 12th 2017)
Permanent pricedrop for both PS4 Slim and PS4 Pro in October.
PS4 Slim $249 (October 2017)
PS4 Pro $349 (October 2017)







