There is feature freeze now for KOffice, so you can expect Deform brush in Krita 2.1. I work on it so it is stable as much as possible and fast, optimized. It works almost the same way the IWarp plug-in in Gimp. There is no support for animation in deform brush and I did not implemented adaptive super sampling.
The main difference is that it is tool. Gimp has it as plug-in in Filters -> Distort -> IWarp. But it is probably TODO for gimp developers to make it tool too.
I also fight with clever GUI. I put some special options that are not in IWrap plugin. You can use non-destructed image and see incremented result. You can also deform the image over and over to get deformed image in “exponentially” speed. There is also support for lens distortions. It gives nice results, reminds me a water drops. But I have to wait for ready filter paintop. It could duplicate it’s function using Lens Correction filter.
So some nice pictures made from scratch: