I'd say he has already taken mortal form as the adoring fan, He just plays dumb and wait for the moment to strike the hero, Nobody stands in his way.
His ultimate plan is to become so annoying that every mortal being starts eating apples and will eventually become an apple their self. And that would be the apocalypse, Everybody becoming apples.
A bit touched by Sheogorath, are you?
Anyway, I don't think Lorkhan is really 'doing' anything. He's just...dead. Not dead in a mortal sense, but languishing idly. I'm sure he's cooking up some scheme for his return, but I doubt he has the power to truly
do anything. However, plenty of recent events all seem to playing into his favor, so either I'm wrong and he
is influencing us, or he's just the luckiest dead person out there.