Due to overwhelming interest, we have no choice but to cap the Championships at 256 entrants. There are currently over 200 people already signed up; I just can’t imagine running this tournament with over 256 entrants. So hurry up, before the final seats fill!
For those that miss out, there is always the Kingdom Design Challenge! You can still end up winning a copy of Hinterlands by designing one of the Kingdoms that will be used in the Grand Final.
Dominion Strategy 
An option is to make a preliminary round. For 256+x players, the lowest-ranked 2*x players would play qualifications, while the other 256-2*x would play directly in the first round
That’s basically the same thing as having more rounds, isn’t it?
Yes, somehow. Only for a few players. There are only 4 registration days left, so I guess the surplus will be quite small