Let's talk Mythical skins

So, let me go ahead and get introductions out of the way, I'm Viperpunk of the NA region. I main Ekko, Vayne, Zac, Leona, and Shen. There, done. Now let's go ahead and talk skins of the mythical quality. Hextech Annie, Soulstealer Vayne, Dreadnova Darius, Lancer Zero Hecarim, Hextech Kog'maw. Now we were told that we wouldn't be able to acquire most of the vaulted skins again. Some examples would be: Human Ryze, Black Alistar, the victorious skins, Riot Singed, and probably some of the most coveted of all the vaulted skins, the Pax skins, (Pax Sivir, Jax, and TF). However, if i'm correct, Riot Singed was released one time after being vaulted, and not again since. Pax Sivir also saw a return in the form of Neo Pax Sivir. My questions to any Rioter willing or able to answer are: Is there a list or an order as to which champions will be receiving Mythical skins, if not, how do you determine what champions will be receiving one, will every champion receive one, and will other vaulted skins be returning in the fashion that Pax Sivir did? And Last but not least, my questions to the community: What skin would you like to have return from the vault like Pax Sivir did, and what champion do you want to see get a mythical skin personally?

I'd love to see a hextech crafting skin for Shen personally. Can't wait to see the community's opinion!