Towards the end of TNG Tasha Yar's daughter Commander Sela has a brief stint as enemy in a few episodes. It always seemed as though they cut her arc off suddenly and without resolution. There are a few novels and such that deal with her more, but I was wondering if anyone knows about any canceled or even coming projects that relate to her? I'm talking major projects like unmade TNG movies and the like.
No, there are no upcoming major projects related to her: the entire TNG section of the franchise was scrapped after Star Trek Nemesis. The only two aspects of that section of the Star Trek timeline that are still active are licensed novels and Star Trek Online; the latter of which is struggling so I wouldn't expect to see anything major to come of it. However, according to the article you linked:
In Star Trek Online, Sela survived the supernova of 2387 that eliminated of many of her opponents and cleared the way for her rise to Empress of the Romulan Star Empire before she was exiled for attempting to assassinate the head of the Tal Shiar.
Star Trek isn't like LOST or other deeply serial dramas: not every character featured is important or will play a huge role except as an entertaining recurring character. Sela was featured in a few TNG episodes, which is pretty good for a recurring character.