As for myself I would really like it also. I have mostly been confined to Paint Shop Pro 8 for most of my editing career (just recently began looking at free alternatives) and have found a trick around it though it requires more skill.
Use the clone stamp at 50% opacity (Percent 50 mode I believe in Paint.NET) and clone over what you want to "heal." Next use the smudge tool (which I don't think Paint.NET has, so maybe use Gimp for this one effect, though I don't really like Gimp much), also at 50% opacity, and smudge around the cloned area until it looks like you want it to.
Currently this is the only solution that seems to work and act much like the healing brush.
