+Arjan van de Ven
The main reason for eMMC was that external SD cards run FAT on them, which is just awful for trying to access/update in a reliable way without making all writes synchronous slowing your phone to a crawl and thrashing your cards number of write cycles, even then, a battery outage can still hose you due to FATs lack of modern consistency mechanisms (logging,journaling, etc). So switching to a real FS (such as ext?fs) was necessary to keep android phones stable and not get bricked every time they suffer a power glitch. once your external cards were no longer compatible with other computers, it didn't make sense to keep them external when it cost more and didn't provide much user benefit.
Hopefully, this will mark the return of external SD cards on phones, a real, free, and open alternative to FAT is needed and this looks like it will fit the bill.