I dig a little bit more in the code and found out the exception is raised at the following line of ./plugins/touch/current/app-build.js (within Sencha Cmd):
Class StBuildRunner is part of sencha.jar so there's nothing more I can do to troubleshoot this further.
var stbuildRunner = new StBuildRunner(),
args = ['package', resolvePath(src, 'packager.temp.json')],
stbuildOut = stbuildRunner.run(args),
exitCode = stbuildOut.getExitCode(),
stdout = stbuildOut.getOutput();
Is there any chance to get a quick feedback about this? Will remote build (through ssh ever be supported ?