Do you know of ICBM (Intel chip based Macintosh) which boot from: APT (ATA Parallel Transport, a.k.a. PATA), USB MSC, IEEE 802.3, IEEE 802.11, IEEE 1394 SBP, and Thunderbolt UTDM?
Apple Mac firmware has awareness of SDIO/SDHC (this instance of SDHC refers to ShitDigital Host Controller, not ShitDigital 32-bit * 512-octet), at least enough to boot from conventional SD cards.