Its good that XBrick is selective with the tokens that can be listed and that they are trying to create a platform for more high-quality tokens. But this may also cause delay in the growth of the platform, traders prefer to have a wide variety of tokens to trade.
Well, the way I see it, the reason being is to make it look more prestige by having only high-quality tokens to start with. But it doesn't end there, Xbrick will select cryptocurrencies it considers to be high quality to be listed for trading from time to time and may charge a listing fee as stated on page 32 of the Whitepaper. This would also create an income to XBrick somehow if I'm not mistaken. They will also run a token voting campaign wherein everyone is welcome to nominate their favorite tokens. As to the delay in growth, well will see how they will play and change the game as the day and campaign goes by.