OpenSync? could be even more open if you were able to run your own program(s) when syncing. Or in other words : I don't care about C and performances, please provide me a mean to write shell / perl scripts to sync my devices/files/whatever.
To give a concrete example of the problem : the only tool able to commnicate with my Nokia 3100 is "gammu". Its output is parsable but is far from being a XML file (more like a text file) and it would be really easier and more flexible if it could be parsed through perl.
To have this feature, I think someone should write a plugin which purpose is to call external programs whenever possible and its configuration file being those external programs.