Replacing GIMP

Though there is overlap, for sure, Krita has a different focus from GIMP, so it'll never be a drop-in replacement. Krita is a painting application, GIMP an image manipulation application. Krita's brushes are better, GIMP has more filters and better selection tools :-)

And these days, Krita is pretty suitable for professional use, it is actually used by professional illustrators, texture painters, game graphics designers, vfx studios and matte painters every day. Check the brochure I made for the 2.6 release: http://krita.org/aboutkrita26.pdf.

And I fully intend to go further down this route, which is why we've got the Krita Foundation, which sponsors development, and my company, KO GmbH, which provides professional Krita support for VFX studios.