I understand WHY the skin was Lux
First off, let me say I as well was kind of shocked that Lux already got another skin as Elementalist was an Ultimate HOWEVER looking through the champions it makes slightly more sense.
Also, ASol players im sorry, It probably sucks to think your main is finally getting a skin before "Nope its for a champ that recently got an ultimate." But also people probably looked a bit too far into the teaser. Its different from the Shen teaser as it was mistaking what was IN the image, instead of what the image was attributed to. As well as it makes sense as it IS the year of the dog.
Anyway on with the reasoning: They wanted a "motherly" character to raise the pups. So lets look at all female champions.
I think that's all of them.
Now how many of those are A. Mature enough to raise an animal, B. A character typically associated with kindness. That narrows it down to...
(A bit at least)
and the 4 mothers of league
. Babysitting their little ADC children... Wel except Soraka, shes probably a closet sadist.
Now lets look at recent skins: Soraka & Janna JUST got skins. Ashe JUST got championship (Yes Esports skins dont count but for the most part there is still a larger wait time than like 2 months)
So that leaves
All of them got a skin in 2016 so there is no DESPERATE champion that can fill this niche (Nami got one mid 2017 but it was esports)
So who fits the theme? Well honestly thats an opinion based thing. I dont SEA Nami raising land animals, and IMO Leona isnt someone that I think that the dogs would PROTEC like Lux, hell she has a GIANT FUCKING SHIELD. And that leaves it, at least to me, between Lux and Sona. But thats just my opinion.
So yeah, its okay to want skins for older champions but IMO the casting of the lunar skins this year made PERFECT sense.
Ezreal which are popular and sell more will always have higher priority on new skins. Same with Rakan
and Xayah