I'm sure Marina Sirtis feels that way and would jump at the opportunity to come back, even if it was just a cameo and she got paid a pittance.
Shatner is a different story. As has been stated before, he's either got to be the center of attention and get paid lots of money, or he's out. This is not going to happen.
Think of it this way: If Adam West suddenly stated that he wanted to play Batman again in the upcoming Batman vs. Superman movie, and he wanted a ton of money and be the star, we'd all be laughing our asses off. Yet when Shatner says the same, we all want to take him seriously. What's wrong with this picture?