Too Human didn't take 10 years to complete.
Silicon Knights is a slow developer, but the TH world is set. Unless they plan on revamping the story again or starting from scratch, a sequel should be out sooner rather than later.
It comes down to priorities. SK supposedly has 3 titles in the works: Too Human 2, a untitled project to be published by Sega, and a rumored Wii game. Since they've traditionally had trouble working on more than 1 title at a time, completing the Too Human series would be the best idea considering the parts SK obsess over are/should be finished (characters/plot). I want Eternal Darkness 2 as much as the next person, but unless Dennis Dyack plans on hiring more people or has learned some time management skills, they're better off finishing whatever is furthest along which is likely Too Human 2.