How Rajhin Stole the Book that Knows is for sale by Filer Ool this week and reminded me of the Ring of Khajiiti, which grants speed and invisibility. I think it'd be a nice Mythic option.

In ESO so far we have the Hidden Moon Band that grants Swift and is part of the Darloc set, the Ring of the Wild Hunt of course, the Shadow Queen's Cowl introduced with West Weald (mentioning just because it exists, but I play in stealth most of the time and don't find it useful; not worth replacing RotWH),

and the new upcoming antiquity on PTS,

Technically you can already get speed + invisibility with NB and/or Vampire. But I still think a Ring of Khajiit would be a nice option for those of us who prefer other classes and don't like Vamp. It would be a nice alternative to RotWH + Potions too. I'm sure there would also be some cases where this is too OP (PVP mostly I guess) and it'd be understandable if invisibility can't be a permanent effect; maybe it can be triggered by an action as in the other cases. But I'm not here to think the whole thing through – that's the Devs' job! Just an idea.