The Little Mermaid and Beauty and the Beast are in the original plans. But they were supposed to be built few years later after the opening (there is actually enough room for the Little Mermaid, even if a placemaking issue would result), but there are no more information. On the other hand, Philippe Gas, Disneyland Paris CEO left some clues on futures attractions, but he may have told that for others attractions, such as Splash Mountain, that fans are more and more demanding (is it grammatically correct? Once again, sorry I'm french). The are some concept arts ( http://i40.servimg.com/u/f40/16/90/17/12/captur11.jpg ). But, the concept is already here, there is "just" a problem with money apparently.
For the Matterhorn, no information, sorry.
Finally, Rattatouille is under construction, but there are other projects comming for the Studios, they are just kept secret, because the Studios will be developed until 2018