His optimal build from my, and many others' experiences, is going to be
into
, seeing as spell vamp is no longer a needed stat. I personally opt in to movement speed quints. This puts my back to 340MS. Trinity and boots pushes me into around the 420 mark, that being around the same movespeed as a Trinity Force Irelia. Alongside this, Mordekaiser gains a 40% slow on all of his abilities, alongside phage from trinity force. Mordekaiser's ult, if needed, would slow for 40% for 10 seconds. Mordekaiser, with this set up, can reach almost any target he wants, outside of wall-hops and things that would trip over current kaiser. This version of Mordekaiser is set up as to allow Mordekaiser to build to catch up to people reliably. Current Mordekaiser does not want to build a lot of movespeed oriented items, because they don't give him as much as other AP items. This mordekaiser can afford to go hybrid.
Then theres the issue of damage. If you build only Trinity and Rylai's, your damage would be lacking, right? Mordekaiser's Q with these 2 items alone at level 18, across all 3 hits, which he can land because of his build, would do about 2200 damage, split nearly evenly between physical and magical damage, with 1 trinity proc.
You can't say "A champion that shouldn't be autoing very much" when new mordekaiser, while he may have the same goal in game, plays differently. New Mordekaiser DOES want to be autoing, as he will be a high damage tanky-hybrid bruiser who needs to auto attack in order to get his full damage off. He also has what may be the highest base AD in the game.
E is no longer the focus of his kit. Yes, his E is weaker in terms of damage in 90% of cases, but you are thinking of mordekaiser as he is now, instead of as he will be. His E damage isn't as important on new mordekaiser. What Mordekaiser wants from E, is a mildly decent waveclear, which, as someone who has used it, it has, but most importantly, an easy way of generating a lot of shield. Mordekaiser's E's damage scales up with levels, so you don't need to focus ranks into it, and then it also generates a TON of shield, as it gives the % of damage back as a shield, AND automatically fills up Morde's shield by 15% per champion hit. During the early levels, Morde can instantly fill up his entire shield with just a single E if aimed properly.
On the subject of W, I hate the fact that you can't solo cast it. I hate it as much as every one else does. HOWEVER, when used correctly in a bot lane, Mordekaiser's W is monstrous. It's an AoE Damage Waveclear Sustain Utility spell. While the prerequisite is ass and SHOULD be changed, the ability itself is amazing when used properly.