If they just wanted to make it a single tournament and it had no correlation with the NGS then they wouldn't be waiting all this time to release it when NGS is out.

I'm just gunna guess you haven't read any of the NGS threads, the roster size is being increased and a points system is being added where each individual member can contribute points, kicking members/using temporary members will bring some form of punishment (losing points most likely) as the whole point is to promote guild loyalty and overall activity in the game outside of towering and guild dedication.

There's no other reason they would be changing the guild system, and taking this long to do so.