Hey there. I realize this is REALLY old, and things perhaps have changed. However, I’ve only ever used the libmayapview.mll file, never having even loaded the libmayasavepview.mll in any of my Maya installation, from 2012 to 2016. For me, (using the MayaPandaTools.mel interface anyhow) The libmayapview.mll seems to perform exactly how you described the libmayasavepview.mll is supposed to. 
Currently, using the interface as I mentioned, Maya will always save out a egg file before running the pview.exe command on it. As well, when running the menu option to view a file, it of course brings up the dialog to choose an egg file. I know I’ve done some modifications to this tool, however most all the original base coding is still entact as it’s been. I mostly did mods to the GUI and added some commands.
~Sean~