So, I've been trying out one of these:

I bought the 16 gb version as it was the least expensive and I knew I had a 32 gb micro SD card in my camera. This item is a wifi flash drive. You connect to your computer, load it up with music, video, photos, etc. and they become available via wifi and an on device app, to your wifi enabled mobile device; in my case a Fire HDX.
I won't repeat the tech details here - check them out at the above link. I will say, it is a marvelous piece of technology. I really like it. My wife has a Fire HD and we both can connect up at the same time and listen to/watch/look at different media. The 16 gb worked fine, so I removed the microSD card and replaced it with a 32 gb card. Again, it performed as advertised, at least with two devices at once. Since I don't have 8 devices we weren't able to test that. Throughput was even and viewing two different movies at once didn't seem to impact playback.
But, shortly after I got this thing 64 gb cards became available. I got an Amazon deal on one and was anxious to see if it would work in the drive as SanDisk says it'll only take
UP TO 32 gb cards. Inserted the 64 gb card ... plugged it into a USB port on my computer and loaded on two movies ... removed it from computer ... turned it on ... and ... nothing. Got an error that said the card needed to be formatted to a file system the Fire can read (that is FAT, for my computer and Fire).

However, after a very short search on the web I found a way to format the 64 gb drive to the needed file system. - thank goodness for user forums (fora?)!! Reformatted the drive, loaded two movies and connected with the HDX and voila! Or maybe eureka would be more correct. Success! I now have a 64 gb wifi drive for our upcoming flight to Colorado. Will load a small part of my movie collection to take with me, and of course a goodly number of books - you can never have too many books on a trip, I always say. The only issue is that there is a 4 gb file size limitation at this time. According to SanDisk a fix for that
MAY become available soon via software upgrade. So far that hasn't impacted me - the movie files I have run 1-2 gb.
All in all, for me, a worthwhile investment. Hmmm ... I wonder when 128 gb micro SD cards will be available?