This is definitely a huge step in the right direction.
Thanks everyone for the positive feedback!
Aside from the simplicity of just editing sentence by sentence, I like the massive help section you added at the top. We have to assume that the average contributor hasn't made more than a few edits.
If you like to read more about the choices made in the top section, I've written it down at: http://www.mediawiki.org/wiki/User:JanPaul123/Sentence-level_editing/Prototy... and http://www.mediawiki.org/wiki/User:JanPaul123/Sentence-level_editing/Prototy...
This will introduce a big chasm in between making a simple sentence edit, and then making a big change like cleaning up a whole paragraph. But that's quite acceptable and we can build on this to make paragraph editors, image inserters, infobox editors, and so on.
Exactly, that is the goal. To 'teach' wikitext by slowly introducing more complex concepts. For now I'll focus on the sentence-level editing though.
Best regards, Jan Paul