It would be nice if there were a tool that would take the input to graphviz, run it to graphviz to get the layout and then use that to generate the tikz code using that layout.
Years ago I wrote and contributed a backend to graphviz that output MetaPost (I just had a look and don't see it in the source anymore). It was very easy; I found another backend and made a few tweaks. Perhaps you might have a look?
TikZ/PGF had a graph layouting implementation for about a decade now, c.f. "Part IV - Graph Drawing" in the manual. And apparently `dot2tex` can also render TikZ instructions, so going via Graphviz is possible too.