I'll throw down a bit of analysis. The thing as I see it about package systems in linux, and I lump them together because they are all of the same design, is they are all based on a database. rpm, dpkg and all their gui cousins manage the database and call the package installer. You hit the site, lookup my distro, version, pkg, file in what arch, check the local database, what's installed, what version, compare to server data. Find which pkg owns which file, etc. etc. Now designing a similar system for PND has a unique situation, no distro package management works for removable devices. The database poses a huge problem in itself, where to locate it. Certainly not on the removable media unless it covers just the pnd's on it and then it's redundant information and flies in the face of normalization since the pnd's are just laying there. A website was suggested, or server, the, 'store', really doesn't need to be more than a website since they are so robust, already written and pass through most all firewalls with ease. Putting user info on the store server is not a bad idea really but the removable media pretty much tanks that unless you uniquely label the sd cards and the app prompts you for them when updates. Hey that's not bad, may talk myself into it but the server maintenance, storage and level of effort is just too much. Privacy issues and user data as a commodity will surely doom such a notion. A naming convention of name-version.patch.pnd or similar might provide enough information from a directory call to take the place of a database.
So, can we add to the unwieldy pnd system with such minmal information and make it as friendly as yum only prettier? Perhaps an app that;
1) List the server's available pnds of the right version of os and installs them on an sd card
2) Lists the pnd's on an sd card and highlights the one's available to update
3) Change the version of a pnd file on an sd card to one on the server
Would be within reach and give the appearance provide the basic functionality of a much more complicated system. The server could rip a page from rpm2html and store the big list of pnd's available in xml to served as pseudo soap, libxml has a very robust ftp/http client in there, was all I needed to close the loop on rpmfind once to perform auto updates. Another issue to consider is security, the poison repository might not be a laughing matter, convenience at the cost of safety might make that homely browser option look a little better.