we need slightly more scum ships per faction imo until the numbers start coming up to unity then three a wave will them be reasonable

They can start releasing three ships per wave with wave 7 and still even out the ship count. Not counting epics, the current count is:

Rebels = 9

Imperials = 9

Scum = 7

In wave 7 they could release three ships:

Rebel / Scum ship

Imperial / Scum ship

Scum-only ship

That would bring all the factions up to 10 ships.

If they go that route, then as much as it pains me to leave the Assault Gunboat out of a wave prediction, my guess would be this:

Rebel / Scum ship = Havoc

Imperial / Scum ship = Skipray Blastboat

Scum-only ship = Could be anything (maybe the Dunelizard or a bounty hunter's ship)