Did anybody investigate what would it take to enable exfat support "unofficially" ? There is at least one GPLed exfat driver and while I understand why Jolla might not be able/willing to ship it themselves, that does not mean users can't do that themselves.

From a cursory look it appears to be quite easy to do:

On Fedora, Mageia and ArchLinux
How To Install exFAT-utils on Fedora 20/19/18/17, Mageia 4 And Arch Linux

exfat-fuse RPM on RPM Fusion

On Ubuntu
How to get a drive formatted with exfat working?
How to enable exFAT in Ubuntu 14.04

That would enable interoperability for users able & willing to do the needed change on their own, without Jolla a substantial sum of money for what basically amounts to a tiny additional "supports SDXC" sticker on the box with the tablet.