How to give Mordekaiser windows of power and thus make him a healthier addition to the game
Mordekaiser lacks meaningful interaction in a solo lane and even his duo lane isn't much better at giving his opponents much counterplay without making Mordekaiser underpowered. This was the core reasoning behind putting Morde bot with the Juggernaut update since he was condemned to mediocrity due to his bully nature and unhealthy patter.
Him spamming E and gaining massive shield was problematic. It was unavoidable poke with 250 base damage on a low cool down and with almost no cost attached to it. It made him almost unbearable in certain matchups and made laning against him a chore.
But this was remedied in his rework His E retained its rather high health cost as well as having had its damage reduced. It was a step in the right direction and with Mordekaisers core problem in mind one could have tried harder to give him windows of power to truly make him healthy in both solo and duo.
So what remains? Mordekaiser's shield gain was nerfed but it's still kinda oppressive. It also lacks downtime. But if you nerf it further Mordekaiser would lose his core identity and become much worse due to him relying on it as a CC/mobility less melee bruiser.
>Mordekaiser needs windows of power regarding his passive Iron man to truly make him interactive in lane and give enemies windows in which they can punish him.
Suggestion:
New: Harvester of Sorrow/Powerslave/etc.(Placeholder name)
Mordekaiser DOUBLES his shield gain for 8 seconds while surrounding himself with metal shrapnel. For the duration he deals AoE damage in a circle around him and increases his resistances by 10%
Iron man: Shield gain lowered from 25%->15% Shield gain against minions only one THIRD effectiveness, down from half
-->This would finally get rid of Mordekaiser's issue of practically being untouchable due to his constant shield gain when around minions but allow him to truly become this nightmarish entity on the battlefield when being under the effect of his W.
It's also harbors some resemblance to his old Creeping death with his resistance buff but by making it a % instead of a flat amount he'll scale harder into late game, something riot wants him to be; A late game champion
It would finally give him windows in which his lane opponent can abuse reckless usage of his W. They can poke him, all in him, hurt him enough to back. Him having piss poor hp/5 makes it all the more rewarding and more devastating for Morde who needs to be healthy in order to use his spells.
He can use it to beef himself up in a gank or all in, he can use it to commit to extended trades as well as just use it for wave clear. This would also allow Riot to tweak his stats more to make him hold his ground but still have his power tied to these valuable 8 seconds.
The cool down would probably have to start high but get lowered drastically either by ability rank or Morde's level to allow him to max out his E/Q for the early game.
With the addition of a downtime to Mordekaiser's powerful Iron Man his laning phase would be much more interactive and reward perfect usage of his W as well as abusing its downtime for the enemy. It would give enemies windows in which they can punish Mordekaiser for simply using his W whenever it's up or simply push the wave but also give Mordekaiser this "Come at ME" feel whenever he uses it to become almost impossible to kill. By removing him almost always being at full shield when around minions he may even be able to have a tad better base stats so that he relies less on the feast/famine play pattern his Iron Man provides.
Stil, there are a lot more elegant solutions to make Mordekaiser more healthy and involve a lot more strategy and give RIOT more avenues in which they can balance Mordekaiser without making him either overbearing or underwhelming.
http://img10.deviantart.net/81c5/i/2012/111/a/9/mordekaiser_by_skullsinacab-d4x3moj.png
TL;DR Mordekaiser lacks windows of power necessary for a healthy laner. Lowering his shield gain and making his W increase it would fix some of these issues without changing what makes Mordekaiser who he is.
vs 

has the same window, since his passive builds by repeatedly pounding minions before switching to a more meaningful target. Was this taken away because it made him immune to poke? (If that's a problem, why not change the shield so that it only intercepts 40-80% of incoming damage, rather than all of it?)