Hi Vinícius. Good examples. Think is a very good addition.
For the bspline there is a branch but still not presented to merge at
trunk because are waiting to a reviewer.
Here is the branch:
lp:~jabiertxof/inkscape/bspline+spirolive
Here is the post in the forum:
http://www.inkscapeforum.com/viewtopic.php?f=11&t=13496