I did the Newton conversions of the early NXE stuff, and let me tell you it's a pain in the behind. It took a great deal of semi-manual editing to convert the text files into something useful for the converter. Truss did conversions of the early Symphony stuff. He used some shell scripts to automate much of what I had done semi-automatically in Emacs, but the results still required a fair bit of tweaking by hand. So, really, it's not likely to happen on any kind of mass scale.

I have a Kindle DX and a DXG. What I do for preformatted text is a simple copy-paste into LibreOffice followed by an export to PDF. The key is setting the page size correctly and the margins to zero. From what I've found from a quick Google search, a good page size for Kindle 3 (6" display) is 5.49x7.33 inches. Set the page size and margins, then copy-paste in the text. Select all and set the font to a monospaced font. I use Liberation Sans Mono Bold; YMMV. Set the font size just small enough to eliminate line wrap. Save it off so you have a copy, then export to PDF. Copy that PDF over to your Kindle and enjoy.

A trick for the smaller Kindles is to set Landscape mode for the base document. The greater width means you can use a larger font size without wrapping text.