Once this is ported, wiring it up for SD cards shouldn't be hard (only difference is the use of ext_perf instead of ext_csd for feature detection, and the renumbering of CMD48 to CMD43 - SD also supports an optional "sequential queuing" mode that eMMC doesn't, but it's not really relevant for Linux).
The Linux MMC/SD stack implements command queuing only for eMMCs, not SD cards, and even then, only for host controllers that can manage queues in hardware. Previously, software command queuing was submitted to the linux-emmc mailing list, but then apparently ignored: https://patchwork.kernel.org/project/linux-mmc/patch/1601195766-26648-1-git-send-email-gray.jia@mediatek.com/
Once this is ported, wiring it up for SD cards shouldn't be hard (only difference is the use of ext_perf instead of ext_csd for feature detection, and the renumbering of CMD48 to CMD43 - SD also supports an optional "sequential queuing" mode that eMMC doesn't, but it's not really relevant for Linux).