[errantblaze]

I didn't realize this was an issue. Does this include flagship phones or is it mostly lower- and mid-range?

From experience, the Galaxy S7 supports at least 128GB (a quick search returns a 256GB max). S6 didn't support microSD, S5 supports 128GB, S4 supports 64GB, S3 supports 64GB.

[SAI_Peregrinus]

sdxc has been in the spec since 2010. Anything that supports over 32GB (sdxc) can support up to 2TB with no hardware changes. I still have an S4 and use a 128GB card, but I've got a custom ROM. Most of the "up to" values for support are simply the biggest card that was available when the device was released, not the biggest the device can read. That's almost always going to be 2TB, the maximum that exFAT can support.