Gede: I'm afraid that I don't put much effort keeping my info current regarding expensive graphic cards. I'm AMD-exclusive due to their relative openness (I hope they'll go that libreboot or coreboot way). But I would like to know if you find the RX480 offers good performance/$, assuming the issues you notice don't get sorted. I expect Vega will be too expensive for me.
Amd's driver is opensource, not just "relative". The hardware is not. All gpu makers (intel, amd, nvidia) load firmware, they just do it differently and at different time. Intel loads it via UEFI, so even if kernel is blob-free there, the blob is still loaded. If you remember, during development, AMD has supplied different firmware for same GPUs, probably they updated so-called "golden bits", writing in GPU registers in special ways to unlock certain features. I think Nvidia does this too, as they once included "safeboot" into GPU that prevented it to load "unsigned" firmware in an effort to limit nouveau development.
I think its very unlikely AMD will go libreboot/coreboot way, because they seem to have implemented software-only version of TPM in firmware (fTPM). This is probably why stopped supplying AGESA.