Raising the points from 300 to 400 is more than just adding in another ship or two... it also changes the way scoring works.
The current tournament scoring rules are as follows:
Margin of Victory Win Loss
0–20 5 5
21–50 6 4
51–90 7 3
91–150 8 2
151–220 9 1
221+ 10 0
In a 300 point game, winning by 221 could mean you destroyed 74% of your enemy's fleet without losing anything. A clear majority and usually a victory by such a margin that it shatters your opponent.
However in a 400 point game, that percentage is only 55% - just above half. That's a pretty significant difference, and now in a 4 ship build, you might lose 2 ships and end up scoring zero tournament points.
I wonder if the point values will change to reflect the cost of new fleets?