AFAIK Android 6.0 and up lets you 'Format SD as internal storage' and from then on it's well, internal storage. I remember messing around with it on my Nexus Player awhile ago. In that particular case though, it did NOT handle unexpected power-downs at all well. I suspect it was a bug with remounting the encrypted filesystem on the card when booted back up next (where a Linux box would normally run fsck on it and then remount). I ended up doing some digging and filing a bug but never really getting motivated enough to stick with it.

FYI at least Samsung seem to be realizing their mistake as their latest models have the microSD card slot again after having abandoned it for some time, so it does seem like it's back.

I also have to concur with what others have said here - I've done my fair share of Raspberry Pi and ODROID-XU4 system image tinkering and come to the conclusion that microSD cards suck big time as a general purpose read/write storage device. I wouldn't feel comfortable having my phone's internal storage running off one actually.

Now if phones came with eMMC slots.... :)