I made a Sally Whitemane Death Knight skin idea, but after a second thought, I think it should be all the three Horsemen that are not Alternate Hero Skins yet. I hope you guys forgive the re-make.
Darion Mograine, who is one of the Four Horsemen, is already an Alternative Hero Skin option for the Death Knight players. So, making the other Three into Death Knight skins has precedent. It would also make sense to have all four, rather than just one of them.
The other three Horsemen are Sally Whitemane, Thoras Trollbane, and Azgrim.
I think the Death Knight skin collection would benefit from these three because they are clearly very powerful Death Knights, they fought in a lot of conflicts and survived them all… well, “surviving” in the sense that they are intact Death Knights.
None of these three are currently Death Knight choices in any way, shape, or form. So, making them would expand the Hero Skin pool into three choices that are completely new. Completely new choices will please the playerbase, which will have more choices, and they will please Blizzard, because brand-new stuff tends to sell copies to the pleased playerbase.
Thank you for reading my idea, and please accept my apologies for the remake.