I've seen documentation of roadmaps and releases refer to the version numbering as possibly up for consideration of revision:

"Evaluate changing the numbering scheme to a date-based one, or setting more realistic goals for major (1.0, 2.0) releases" <http://wiki.inkscape.org/wiki/index.php/Roadmap>

I can see the next major release after 0.48.x as a candidate for change as the "9'er" may lend itself toward a new scheme.

• 0.49.0 --> 0.90.0 (followed by 1.0, 1.1, 2.0...)
  
• 0.49.0 --> Inkscape 9 (followed by Inkscape 9.1, 10.0...)
  

There have been a lot of excellent developments to be release in the next release, including C++, cairo, alignment/distribution along with new possible builds on win64-bit (Partha's help), and native Mac OS X (some almost-ready builds are out there).  If these all reach maturity for the release the new builds are providing an increase audience and userbase.  A changing version numbering scheme could reflect the developers' acknowledgement of this and demonstrate the activity of the software project.

Just IMHO,

--Jared