So Im pretty sure this is like my fourth or fifth thread about Skarner since the Juggernaut Update back in Season 4 or 5, so I wont be surprised if this gets downvoted into oblivion just based on subject and author alone.
However, as opposed to focusing exclusively on modernizing his mechanical kit and putting bells and whistles on it, like usual, I'm going to start with something far more important as Skarner has always been a mechanically interesting champion simply because of his ult: Skarner's Lore.
To give a scope of how much a lack of lore support has affected Skarner, one only needs to look at his history in terms of both mechanical buffs and nerfs and also skins. Skarner actually had a Legendary Skin, as well as three other Epic or lower skins, but the last to be released was the Sand Scourge one a few years ago. And his buff/nerf history has been pretty barren as well, with occasional power spikes here and there. I believe this can be contributed to how barren his lore is and how little of presence he has with other champions, especially those from Shurima. Even Rammus, a champion that is similar to Skarner in a lot of ways, even has the occasional nod to him.
One solution would be to incorporate the Bandits mentioned in Skarner's current lore a bit more; after all, Sivir was/is one herself, which could open up more interactione with the other Ascended and Xerath. Another could be to incorporate Void/Darkin/etc elements as well; I dont have an exact idea of how old Skarner is himself, but Shurima has interacted with several other factions over the current timeline from Icatha, the creation of the Darkin, and even Noxus when Cassiopoeia and Sivir freed Xerath and Renekton and revived Azir. In fact, a void or darkin presence would actually make for a better explanation for being so hostile upon waking up than, 'he was young when he went to hibernate'.
Though that doesn't provide anything new for him mechanically, it does allow him a better chance of getting more attention over the game's lifespan as well as provide a better basis for a visual update; Skarner could very well be tainted by Ascended/Darkin blood, or the years sleeping beneath the sands of Ithaca have completely warped his mind and appearance.
Now, as for mechanics, and anyone who even remembers Skarner will know what I will say here: the current passive is a complete balancing nightmare. However, I think it has some merit, as the buffs the spires provide are actually crucial for Skarner as jungler.
My proposal is as such: remove the spires themselves, but give each Brambleback, each Sentinel, each Scuttler, each elemental Dragon, Herald, Baron, and Elder Dragon one stack of crystal loot. When any champion takes down a neutral monster or an opposing champion with these stacks, the victor takes them for themself.
Starting out, the stacks would only provide AS and MP/5 to Skarner himself, but after the second or third clear or even after the first clear and a successful kill on the enemy jungler, Skarner will get more utility buffs like MS, extended vision, and even true sight at high enough stacks.
But what would non Skarner champions get? Well, I would actually suggest they get the MP/5 buff themselves at the very least, but at high enough stacks Skarner will have true sight of them at all times (due to his affinity to the crystals themselves).
Granted, I don't really know how to balance anything I suggested here, but that is why I prefaced this with a call for a lore update; Skarner has potential mechanically as is, but without some sort of story to bolster his popularity enough to be noticed outside of the game itself, he will be put on the backburner a lot.
TL;DR: Update/Rework Skarner Lore, Visuals, and Passive.