See odroid-c2 diffs · GitHub for a comparative diff of the working (left) and current (right) dtb files. This flags only two changes in the dtb, neither of which has any connection to emmc.
Change #1: arm64: dts: amlogic: misc DT schema fixups · torvalds/linux@d9421d6 · GitHub
Change #2: arm64: dts: meson: set 128bytes FIFO size on uart A · torvalds/linux@a270a2b · GitHub
The only other thing which touched mmc (on GX devices) semi-recently is arm64: dts: amlogic: Assign a fixed index to mmc devices · torvalds/linux@ab547c4 · GitHub but we mount the first partition using disk labels not /dev/mmcblkX devices and it's present in both dtb's so it's not relevant.
So
1. USB is an on/off problem with C2 in the upstream kernel so it's possible OTG isn't working this kernel cycle. I'd expect to find issues with devices being hotplugged.
2. I don't see the USB ID's in the kernel driver, which is a simple patch you can test next time I build/push an image update.
3. No HDMI device is deliberate since we don't support IEC958 modes in dw-hdmi yet (no pass-through) but the "Analogue" output works with HDMI fine (output is multi-channel PCM). I'm still tracking down an issue where 48KHz media doesn't output unless Kodi audio configuration is forced to 44.1KHz (used fixed mode). I've seen this on WP2 (also a GXBB device) but not GXL/GXM devices. I've no idea what the issue is.