One thing that I always feel is missing from Pattern Keeper (because let's face it your app is definitely going to get compared to Pattern Keeper) is the ability to "goto" a particular colour. Like if I'm working on a big pattern, and I've been disorganised as per usual, and now I only have 10 stitches of an awkward colour but they're all spread around, it can be hard to spot them. Being able to just auto zoom from one to the other would be awesome.
That might be a completely unachievable feature but just thought I'd throw it out there!