Getting back on topic. The
LikeBook Ares has the same SDcard 128GB reader as the Mimas and isn't quite that expensive.
What's even nicer: I remember the Kobo line being marketed as limited to 32GB cards. However, I had a 64GB sdcard internally and a 128GB externally. So it is a good chance that these LikeBooks are garanteed to work up to 128GB. After that it's what you are able to pull off.