The binary blob isn't necessary, there is a read-only kernel driver for exFAT and a read-write FUSE driver for exFAT, though the FUSE drive is beta software, however since Maemo already has FUSE support, and FUSE drivers are userspace (not part of the linux kernel), it should be trivial to get the FUSE driver working on the N900 should we need it. The "for-pay, closed source, binary blob", is a proprietary driver we don't have the source code for and we need to pay to use it. But as I just mentioned that isn't the only option for exFAT support. To further clarify, the SDHC spec only supports cards up to 32GB, the SDXC spec supports cards up to 2TB, but it also specifies the filesystem to use to be exFAT. In theory, there should be no problem with them on Linux with current card readers, but the only SDXC cards available are full-size (not MicroSD size like the N900 uses) and quite expensive and I'm not aware of anyone actually confirming this, the only issue should be exFAT support, which is where you might want to format the card to use a different filesystem, but it is likely you'll also have the option of just installing exFAT support.