So I'm fairly certain Sion nerfs are incoming.
And while I don't want to see them as a sion main who used the champ to carry himself to plat this season, sion's pick rate has nearly doubled in a single patch, accompanied with a winrate boost.
With this in mind, I'm going to make some suggestions.
1: (Obvious) Nerf his e again. Sion's E is the most important ability in his kit contrary to popular belief. It's the only reliable ability in his kit and it has a potentially very long range. This ability's damage has been buffed due to the introduction of the comet rune, and would likely receive a damage nerf (-20)in the early ranks, or a cooldown nerf (1 second) at rank 1.
2: Nerf his w. His w got some pretty nice buffs right after the disgustingly awful tank update, with good reason as well, however some champions can't pop the shield now in the early ranks. It's not by a lot, and his shield used to be so awful that you sometimes would t put points into it until level 4, even with the health gain passive. So perhaps a nerf on he shield value (1%) or increasing he cooldown (1 second) would work.
3: Nerf his Ult. His ult also got some buffs somewhat recently, but that was to its damage which was pretty pitiful for such a difficult ability to land. But nerfing the damage wouldn't do too much except make experienced sion players win less, so instead increase the early damage again (100 rank 1) and increase the cooldown (20 seconds) to reduce his roaming potential early, one of his greatest strengths, but still reward experienced players for landing good ults.
4: Nerf comet. A significant contribution to Sion's current power is his great synergy with comet as 3 of 4 abilities can proc it reliably. (f you couldn't tell by now getting more reliability on sion is massive. Comet itself is also used on a significant number of other champions too however, and all of those champs who use it have cc on the spells that proc the effect. Therefore, perhaps comet needs to do less damage if the ability that proced it also provides cc of some kind, slows included. (-30% damage)
Once again I'm fairly sure riot sees the influx of sion players and plan to do something about it, and while I'd like to see the big boi choo choo be played in the LCS, I'm certain it should never happen if he's balanced for yoloqueue. I'd most prefer a nerf to comet above any other nerf here, but these are the suggestions that I have as a sion main.