A fresh update regarding the Gigabyte board, looks like it's coming end of June.
So as it stands, seems like late June/ early July is a perfect time to build a tiny mITX AM4 build, as boards from Asrock and Gigabyte should be already out everywhere by that time, and Noctua will have the nh-l9a SE-AM4 out too for those building in a SG13, for instance.
I almost pulled the trigger on the Biostar boards but since I'm waiting for that Noctua cooler, I might as well wait for the Gigabyte or ASrock boards, if only for quality, audio and built in Wi-fi.