The current standard tops out at a clock of 6.144MHz which is exactly enough to carry 24-bit 48Khz 2-channel uncompressed audio in a 32-bit, differential Manche

The current standard tops out at a clock of 6.144MHz which is exactly enough to carry 24-bit 48Khz 2-channel uncompressed audio in a 32-bit, differential Manchester encoded frame that includes sync & signalling bits. Running AC3 and DTS over this is a bit of a hack, but it's a standardised hack. HDMI supersedes S/PDIF so comprehensively that the S/PDIF standard will likely never be substantially revised. There's no compelling reason to invest in the R&D.