SATA on BeagleBoard

Has anyone produced (or planning to produce) a SATA interface for the
BeagleBoard as an expansion card? Is this even a practical proposition?

Your best bet is USB to SATA. The only other option might be MMC to SATA, but this would take some work to get going. The -xM has an extra ULPI interface brought out on a new expansion connector that could be used to implement a USB to SATA interface which has been discussed. No definite plans in place at the moment to undertake that effort.