Never used litetween so I cannot tell (I though it was used to move from point a to point b), but paster would clearly be nice to have (split screen, screenshots, the possibilities are big), however as long as the canvas plugin cannot fully take advantage of webGL, it is a big No for me.
but then again, officially supporting these is not a requirement, sure that gives the security but I would rather see a "built in store" inside C2 and on the scirra website to track easily addons update, install them easily, see the last C2 version they were tested with, different categories (like beta, movement, behavior, plugin, effects, etc..), changelogs, etc.. would be much more useful than filtering everything into an official support, that could even help installing them if needed to open a capx.
since right now, keeping track of 3rd party plugins and behaviors is a chore.