An interesting reason this isn't an included option on a lot of the nav systems is simply one-way streets and a liability concern if people weren't sharp enough to realize that reversing their route would send them the wrong way.
I found mention of this on some other forums and frankly it makes sense if you consider the IQ of the average citizen these days.
2008 TE610 - "Jumpy"
2001 KLR650 - retired "Lumpy"
1987 Honda Saber - destroyed "Crashy"