There's a large chance that they'll eventually release Star Trek: The Next Generation
on Blu-Ray with proper HD transfers and either newly created or newly recomposited visual effects. It remains a very popular series and Paramount is well aware of its financial potential. There's a long and heated thread in the TNG forum about the issues surrounding this.
Star Trek: Deep Space Nine
and Star Trek: Voyager
are less likely candidates for Blu-Ray release in the near future, since they were never as popular as TNG.
Star Trek: The Animated Series
, like its live action counterpart, could easily be remastered and released on Blu-Ray, but whether there is demand for this or not I have no idea.
was mastered in widescreen HD, although the visual effects were upconverted from 480p as it was too time-consuming and expensive to create them in 1080p resolutions. It is often aired on television in HD and could very easily be released on Blu-Ray in this format. If they wanted to re-do the effects at 1080p (unlikely) it would take more work, although, as the most recent series, this may be the most doable since the CGI models, etc. are more likely to still be around.