I know Nathanael and have chatted plenty with him over the years on the subject. We're trying to solve different problems really in the field and I really hope he achieves what he wants.
We've got pretty good performance so far ( faster than System.Drawing in many regards and we know how to improve it further) and a great feature set but we still have a lot to do.
https://github.com/JimBobSquarePants/ImageSharp/blob/master/...
I'm personally working with another chap on ICC profile support just now which is very complicated but will give us a full color management system once finished.
While I figure that out I'm hoping that some of the performance gurus out there will step up and offer to tweak the library where necessary.