Just to add to this, as I feel this could go back and forth a few times, and the dev may claim I’m wrong or I’m misinterpreting the EMMC specifications or something 
Take a look at the following,
and a datasheet for an actual EMMC
If you skip to page 12 where it explicitly states the power supply voltages of VCCQ maximum is 1.95V
This is just one of many examples of EMMCs not supporting 3.3V on VCCQ, and while there are a lot on the market that do explicitly support VCCQ at 3.3V (and some which don’t but will tolerate it) it’s not always a given…
Just a few other points to note which limit mmcblkNX device functionality, say your working on a Switch Lite, the EMMC is soldered to the board, you point to point wire up to the relevant points but you would potentially kill the EMMC (if it does not tolerate VCCQ at 3.3V) and you would likely risk damaging the rest of the board as your basically applying 3.3V to what is normally a 1.8V rail… I appreciate this isn’t the intended function of his device, but had VCCQ been operating at 1.8V then this would be possible, and useful.
EMMC ICs aren’t particularly very tolerant to hotplugging at the best of times, but I’ve found there far more eager to die when VCCQ is at 3.3V… you might be thinking “I won’t htplug it” but in the real world, when some junk get’s stuck in the connector or your USB connector on your PC is a bit sloppy, your inevitably going to hotplug it at some point in time