Yeah, well, the desire to make proprietary and profitize these cartridges would be enormous, like console makers have done in the past. I don't really see that as a positive development, just another blow to my nads/wallet, honestly...I read the 'cartridge style approach' as meaning flash storage provided as blank cartridges you could plug in and download/install to.
SD cards are fuggin slow; even the fastest SD cards are very slow compared to M.2 drives especially, and even SATA drives, particularly on small random accesses. (And writes in particular, not that a console would be writing randomly a lot... ) Also, fast SD cards are quite expensive, and cheap SD cards are typically bottom-barrel dredge quality flash chips and have unpredictable (read: bad) performance that will lead to slow loading and poor gaming experience, and may have very bad data retention performance as well. USB flash devices are largely the same; huge spread in quality, performance and price, but generally much worse in the first two categories than proper flash drives.Even the tiny SD cards are up to 256GB now and lining the side of the box with USB ports or SD card readers wouldn't be difficult.
I seriously doubt a console manufacturer would want all the support headaches from customers using bad flash drives, ending up with really slow loading or data corruption and so on.
Only the fabrication of Flipper was done by NEC, from what I know at least. All the actual IP and other chips came from other companies.i.e., Nintendo wanting NEC in GameCube