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.