First off im not talking about the kinda ok ones like Corporate 
or Firefighter 
Im talking about the REALLY bad ones which are:
Magnificent 
in Wonderland
Ice Tobaggon and Red Baron 
I dont really expect them all to be 1820 tier legendaries but maybe updating them to 975 tier legendaries would be nice. Cause right now these "legendary" skins feel like 520 tier skins
How about Gentleman 
?
Demonblade 
?
Br
?
Even Blood Lord 
?
I feel like they would only update them if that champ is getting reworked. Hopefully they will get updated but I don’t think it will happen soon
are in the top priority for being given full VGUs, meaning all of their skins will be redone from 0. Expect to see Corki's skins to at least get Firefighter Tristana treatment.
They could release Firefighter as a 1350 just like they did with Astronaut
she has nice vfx and sfx
For some reason Riot is against repricing skins or taking things out of the vault so doubtful they will be improved much, even in the case of a VGU, they would become vaulted again after 2 weeks.
I have a special place in my heart for that Red Baron Corki. I like it the way it is.
is listed as a High Priority for a VGU.
SO YES! THEY WILL GET UPDATED :D!
But not until he sees his full relaunch in the next 2 - 3 years.
As for Magnificent his kit and abilities are at a comfortable position that Riot has no reason to touch him. His animations and model are a little basic though, so it's a potential, but not soon.
As for Annie in Wonderland, She actually received her full VGU already, and as a result it's doubtful we'll ever see that skin updated.
I'm still waiting for them to update Forecast Janna. One, it doesn't even look like Janna, and two, if you've seen the model up close the face looks like she woke up from a hangover.
They're like cultural iconic skins really. Many people like the option of an old look that's been taken away as the game goes on. I'd imagine if the champion got a rework, the skin quality of those particular ones wouldn't improve too much, but the other skins would certainly.
That would be nice but I wouldn't hold my breath.
I'd also like an update to Aetherwing Kayle (at LEAST the voice, the current one almost feels like Taric's old VO in terms of length/variety) but seeing as Kayle is eventually up for a rework with Morgana, I doubt they'll touch her any time soon. At the very least we know Akali and Nunu are next for VGUs, and another champ that will be announced soon, so I'm not too hopeful (I feel like you'd want to hint that they would be a combo pack)
I feel like they're doing better on these legendary skins nowadays, but unfortunately, many of the champs already got VGUs and thus won't see work for a while. It's a shame, really.
First off im not talking about the kinda ok ones like Corporate
I dont really expect them all to be 1820 tier legendaries but maybe updating them to 975 tier legendaries would be nice. Cause right now these "legendary" skins feel like 520 tier skins
I actually have both tristana skins and I prefer the firefighter one But I must agree that Nunu Bot and Gentleman Cho'gath are a joke beside->nunu laugh/cho'gath voice
Honestly I think it is more likely that Riot would reduce their prices eventually,because removing these skins from the vault is likely never gonna happen(as they would loose their status as "exclusive" skins) and making these skins into full legendaries(or just making them better) is likely not considered worth it if they are rarely avaliable in the first place.
Ice Toboggan Corki looks like it legit came from a 2000's computer game. It has, in my opinion, "super good splash art".
