The game has dozens of mentions of other classes' companions and various events that could help place them in a timeline. TOR's tvtropes page has a few mentions(JK companion Doc once dated Agent companion Kaliyo, Smuggler companion Risha is childhood friends with SW companion Vette). I'd love to see someone compile these little bits of info to approximate as close to a timeline as we can get. Plus the already mentioned one of the SW story's ending taking place after the JK story ending.
"Sir,we are beginning our search for these rumored 'underwater villages'.They will not stay hidden for long". -Battle Droid Commander OOM-9!