Currently a 1TB Samsung 970 PRO(which only has 3.5 GB/s read and 2.7 GB/s write, way less than the 4.8 GB/s they cite) is over 300$, even with the bulk and resale discounts they get such expansion storage wont be cheap, especially since there will be an extra tax due to there being no other option aviable.
Since when did the launch Vita have a sizeable internal storage ?
Sizeable is relative, and even 1TB is not all that much with current gen games, not to think of next gen games that will probably well over 100 GB a pop.
Sony will almost definitely take the same approach. Next gen only games will be made with SSDs in mind
There is a big difference between SSDs, and Proprietary SSDs.
Unless Sony and MS use the same standart, its gonna end up being an expensive format of storage, simply due to the comparably low volume made.
Consoles sell 10s of millions, but SSDs sell much much more.
In Q2 2019, SSD shipments were higher than Lifetime Xbox 1 shipments.
Even if PS5/XBSX share the same module, and sell 100m each, that would still only be around a year of shipments of regular SSDs.
To make storage affordable you need to have huge numbers, and these simply wont be had at the numbers consoles sell
