A few semi-relevant thoughts ...
(1) Inkscape can open PDF files and save as SVG. This is similar to the NX-CGM-Inkscape-SVG route that Cowski suggested. I don't know which one would work better.
(2) Find a drawing program that can save SVG and can accept WMF (Windows Metafile) data via Paste from the clipboard. When you do a "Copy Display" with NX in the right mode, WMF data gets placed on the Clipboard, ready to be pasted. I don't think InkScape supports paste of WMF data from the clipboard, but I'd guess that there are programs that do. Illustrator, Corel Draw, maybe.
(3) I have some code (somewhere) that goes in the other direction -- allows you to import an SVG file into NX. It's not very difficult as long as you restrict attention to simple shapes. My guess is that going in the other direction is just as easy. What kinds of data do you want to export?
I solved it with a batch file in plotting, render then execute,
in this batch I used the postscript output and converted it with ps to edit or ghostscript to svg.
Look at the ghostscript sites on the web...
Other solution with hpgl output from printer with freeware hp2xx
@%HPXX_DLL%\hp2xx.exe -truesize -r270 -m svg %neul%
to give you an idea,
the plot configuration you have to do is nicely documentated by didier:
If you want everything (curves, bodies, text, dimensions), then using low-level plotting output seems like a good approach. I would guess that you could get it to work with Postscript, HPGL, CGM, or any dumb vector format. Whatever route you take, you'll end up with a very large collection of straight lines in your SVG file.
If you're just going to display the SVG file, and never edit it, then this is fine. Even simple edits (like deleting lines or changing colors and widths) might work OK, too.