What do you mean by "support"? Advertise support during the sale? Hardware supports physical cards which are larger than 32 GB. And OS supports them as long as you don't use exFAT. So if that's all that matters Jolla can avoid getting in trouble by not advertising SDXC support. Isn't it the case with the handset already?

There is no solution which has complete interoperability except for FAT32 (at least today). exFAT is not universally supported either. So whatever filesystem you would chose besides FAT32 today, it would be already not interoperable fully. So the question is, what is the best option to chose if you need to use files larger than 4 GB. I guess it would depend on the use case. Camera users might care about it being exFAT. Others not, since they aren't limited by cameras' restrictions and rather limited by not being able to use exFAT somewhere else.