512MB boards can probably boot but won't deliver a good HTPC experience so we have no real-world intention of supporting or encouraging their usage. We intend to discontinue support for similarly under-resourced Raspberry Pi hardware with 512MB in the near future too.
There are about 10 distros that claim they can run on older pc, even with 256MB ram, and what i noticed about librelec is that it have a very small footprint and that is much to its credit. when idle librelec and kodi consume only half of ram on my Opilite and i didn't noticed particular problems when watching supported video formats.