There are hints in the SWTOR Encyclopedia in the faction sections that cover all four base classes (interestingly, Smugglers and Bounty Hunters are discussed not in the Republic or Empire sections of the book but a third one devoted to the Underworld).
In addition to the character classes, the Republic section also goes into some detail regarding
while the Empire section includes a lengthy section on
. While of course it is possible that these were placed where they were simply to round out descriptions of each faction and its assets, they were included in the same manner as character classes, missing only a description of the class starship and profiles of class companions.
So those two are at least possible new classes coming at some point. The Lore is already there.