This may not be a popular suggestion, but I throw it out anyway.
I think that in 9.1.5 they should add domination sockets to the vendor in Korthia, so you could buy them with catalogued research. They could be much more expensive than regular sockets (maybe cost 10k or something) and maybe require some kind of reputation (maybe tier 6 on one char). But I think it would be a nice option.
I think it feels bad for people to get a m+ upgrade from vault, and then you have to choose between a lower level item from heroic with a domination socket (most people will never do mythic raiding) and a higher ilvl from m+. The shards should still require raiding though. Just a QoL change when the patch is already kinda old.