dke
Before I went 64 bit with Sonar I used a small DX plugin called PitchWorks that worked really well in real time.  You could change pitch, and/or tempo separately or together.  I could place it on the Master buss and affect all audio or use it on individual tracks.  As small as the plugin was (628kb) I can't imagine there is really that much to implementing varispeed.  Heck I think it would almost be better to have it as a plugin personally.
 
Dan

 I tend to agree for what I would want from it.  Something that simply looks like a plugin on the master should be able to accomplish this - of course I'm not talking "automation" etc.
 
I used to use REAPER for slowing down passages to learn riffs etc until I got "Riffstation" which has the ability to slow down and preserve pitch.   
 
The other thing I still use REAPER for occasionally is to *record* a passage at slower speed (beyond my ability) then set it back to "normal".  Works great as a "cheat".
 
I (personally) don't care about any 'chipmunk' or pitch shifting/correcting stuff.