"Fancy" transitions (ie: more than fades and crossfades) is on the roadmap/on the "pitivi love" page on the wiki, and has been suggested as an idea for summer of code projects. However, nobody has been assigned this task so far.
One of the things going on this summer with the SoC projects is integrating GES (Gstreamer Editing Services) into pitivi. GES already does have support for all those transitions, as far as I know, so integrating "fancy" transitions in pitivi afterwards would probably be much easier.
In the end, it depends on having someone come up and "Just Do It".
About donations: the problem is that I still haven't figured out how to process them and what to do with them! https://bugzilla.gnome.org/show_bug.cgi?id=629924