The Nokia #N900 apparently will take a 512GB card (Samsung Evo Plus) too.
It doesn't show up in #Maemo 5 because it was formatted as exFAT out of the factory.
We still didn't know the maximum SD card size that this controller can take, but I assume it'll take up to 2TB.
(according to the SD Card Foundation, SDXC supports up to 2TB)