Propbeanie,
Vega code was in the kernel before the cards launched, not all of it, but several things.
RX480X/580X are supported now, Vega last time I checked, was up to the level that all the other cards are.
When AMD scrapped FGLRX (Catalyst/Crimson) for Linux, to work on AMDGPU, they couldn't "open-source" the whole driver, as some functions were from 3rd-party software.
So they are working on AMDGPU a piece at a time.
For example, no HDMI audio right now. But that's ok, I'm running PC speakers through the Mother Boards on-board sound, so I can use my headphones.
Everything else is supported. Ryzen has a few issues with compiling under heavy workloads, but I've read of several updates to the compiler to fix the problem.
Not much to worry about, I very rarely compile anything. As I'm not running a Linux distro that I have to compile everything. Fedora does that for me.
Other than that, no issues to note, except $. But then again, that's always the issue.
Even if it's just "Renown" is SH3/SH4... Never enough 'money' for your toys!
Barracuda