So, warp cores. Warp cores are a thing in Star Trek, but up until very recently they haven't been much of a thing in Star Trek Online. The upcoming Legacy of Romulus expansion will change that by adding cores to every ship in the game, according to the latest STO dev blog.
Systems designer Jeff "AdjudicatorHawk" Hamilton pens the diary, and in it he talks about Cryptic's desire to alter the feel of STO's space combat ever so slightly while simultaneously providing captains with new tools for both exploration and conquest. If you're fond of space combat the way it is, though, don't worry. Hamilton says that the new warp core mechanics can be "largely ignored at little cost" if you prefer.
Either way, you'll probably want to read up on all the little details at the STO website.