Although xv is no longer actively developed by its creator, I believe there is an active community still adding functionality. Indeed, one of the links you supplied would indicate that is the case.
Nevertheless, as alternatives, I use kuickshow to display my images, but it has limited editing capabilities (rotate, flip etc.).
How much editing do you foresee necessary? Perhaps ImageMagick (www.imagemagick.org/
) can do what you need? It's a pretty powerful suite of applications.
A quick google also threw up netpbm (http://netpbm.sourceforge.net/
), although I've never heard of it.