after extensive gameplay with the latest morde, I can say that he's in an OK spot right now.
he's still a champ that completely lacks mobility, but at least he has a functional W in a solo lane.
so he's pretty much where he used to be (toplane). strong lane presence with clear strengths and weaknesses, and has clear counterplay in lane.
his midlane is still fucked with the nerfs to his E. he can reliably play toplane against most melees, but still loses to the melees that are just overall cancer to deal with (xin, volibear, jax, and olaf, for example)
my suggestion? revert E range nerf, and throw in slightly higher AP/base ratios on his E (not much, just a tiny bit to make midlane possible again). other than that, don't touch him.
good thing that it took months to give morde his second ability back. no, I'm not bitter, why do you ask?