I figure that it will leave the current SM and IN lists badly out of balance. I anticipate character ships that are overpowered for their prices. Possibly some new cruiser or SC pattern not previously seen. And a new battlebarge that somehow will make the original SO look positively balanced.
I also think we might see an old space fleet ship or two make a return. And we might see fluff re SM and lances get shaken up, since that's the direction that most of the non-BFG fluff has been heading. We may see Chaos strike cruisers and battlebarges, as well as marks of chaos for space marine ships that have fallen.
Another likely list would be the fleet of the Tyrant, which would be a hybrid such as Armageddon.
We might also see chapter specific BFG lists for some chapters, such as Minotaurs, that specialize in anti-ship operations.
I also anticipate some sort of strange new weapons.