A small, and possibly OP, change to Sion that would make so much sense.
Is there any possibility of changing the damage on Soul Furnace from "+ 10 / 11 / 12 / 13 / 14% of target's maximum health" to "+ 10 / 11 / 12 / 13 / 14% of Sion's maximum health"
It just...makes so much sense. Especially with how the shield itself gets stronger the more HP he has. Even if they have to lower the ratio a little I think it would be a great improvement to his kit.
. I just think that if he is able to** cc **sooner people would think less of him being unreliable as a tank. As for your idea with the armor pen, that would be nice for pushing Sion into the Juggernaut side. I think his E could be made similar to Cho gath's shout instead of being a skill- shot to push minions. Would make a more dangerous front liner.
These champions do a seemingly better job than Sion all-round.
, arguably 
is closer to
kind of champion.
Well at least he's played competitively as a tank.
(which is kinda core on Sion).