It was revealed in the GDC presentation: external usb support for ps4 games, of course you can transfer them to ssd also, and take full advantage of the new stuff _ i will absolutely do it for the one or two games I'll be playing at the moment, it's a pretty rapid process and probably will be improved.
For ps5 games there's a Pcie-4 expansion slot, so no proprietary cards. Like Oddvintage said, Sony can still produce and sell it's own costumised NVMe for the expansion, and maybe even sell it for PC market _ because it would be still using standard pcie-4 Nand slots, not proprietary like XSX.
Sorry mates but this had to be said: Sony does it, it's ARROGANT greedy Sony ripping of the consumer, they set Vita up for doom and dead on arrival _ well, it doesn't matter because (like someone said yesterday in one of the DS5 threads), we all sheep and if Sony wants, they can sell us a turd and we will buy it, like we will buy the weak hass variable clocks turd, and the ds4 rip off with no 3,5 jack!
But in the other hand, Ms do it and it's a right choice! A expensive proprietary solution will help to offset the cost of XSX fantastic decision! It's a high quality plug and play solution, and Microsoft is SUPER CASUAL FRIENDLY _ NVMe needs a manual to install and Sony won't have compatible SSDs for a year or two, so we fucked and will get variable clocks and only 800GB for the games (where did you ear Cerny saying that on GDC? He clearly said that will be updating us with the SSDs later and that they are being tested)!
Now tell me honestly how does this comes along? It's double standards mates, Sony is always back to being arrogant, everything is in the edge of anti-consumer policy... Microsoft is super friendly, and pro-consumer lots of choices, and honest (that's the new shit around here, they are really honest unlike Sony of course, because they revealed more about XSX, i mean, wtf?!) even when they go with old Sony arrogant, anti-consumer practices... everything is pro-consumers.
And before someone comes with the obvious 'it goes both ways', of course it goes _ like ps plus becoming mandatory! But im pretty sure that never heard anyone calling it a 'super friendly whatever' thing... maybe trying to defend it was a necessary evil to improve the shity PSN state. Anyway that's off-topic and we're taking about next gen drives.