Plasmoid installation (Score 1)

That's a misconception. Plasmoids can both be installed through your system's package manager (just like basic plasmoids that make up the desktop interface are), and starting with 4.2 also through webservices (Those of course only works for non-compiled language plasmoids such as Javascript, Python and Ruby). A security mechanism for installing them through webservices is in place. It'll probably also be possible to share plasmoids among users, to just drag+drop them from a webpage onto your desktop, panel or sidebars. The system is quite flexible.