What would you add as a 7th/8th/9th/etc siege class? It's possible to have more than 6.
We can make special classflags/features using base_entranced, so go wild. Or just stick to base stuff if you want. Specify if different variants for offense and defense.
The goal is to make something that's not game-breaking, though. Make sure it's balanced -- no "LOL saber-immune guy with 900hp, grip3, detpack cannon, and swoop spawning ability LOLOL" garbage. Should be something you wouldn't mind playing against, and should integrate with the 6 base classes.
Here's a couple I came up with:
Tank: close-combat specialist
200 starting HP
85% speed
Pistol, melee
4x melee damage (40dmg/hit = 3-hit kill against 100HP classes without bacta)
Assassin: surprise attack specialist
50HP
125% speed
Disruptor, detpacks, pistol, melee
Mind trick 2, jump 1