After two weeks of intensive research, finally I finished a functional version of a video export plugin using the Theora library.
Ok, but what does it mean? Well, that now users can choose between two different resources to export their animation projects into videos: the FFmpeg plugin and the Theora plugin.
Ok, but just one video export option shouldn't be enough? Unfortunately, the answer is: No. Why? Well, the FFmpeg project includes support for proprietary video formats like AVI and MPEG (among others), which means: potential patent allegations.
On the other hand, the Theora library is focused on one open format (OGG/OGV), which makes it a project free of legal issues related to software/format patents.
Now, this is the nice thing about freedom: both plugins will be included as part of the Tupi source code, but finally users will decide which plugin they want to use! :P

The plugin's code is already available in the git server for desperate testers. If you prefer to try a stable version, then wait for the next revision ;)