With the current system it could only be done with 16 guilds, not more or less. Honestly i think its a fair system.
If you think about it, each guild at their max holds 200 players, if im not wrong. Of course only 50 play the gw, so doing the math, 16x50 = 800. Thats 800 players that have that right every week.
If you really wanna play gw you can either join one of the best 16 guild, merge with one or just try and improve the one your in.