What an amazingly lame, late, and half-baked nerf hammer this change is. It will accomplish nothing desirable. This will not remove the dominance of the most powerful guilds on a map. It will not make it easier for little guilds to break out. It will not remove the 24/7 monitoring for GbG leaders to keep in relationship with their allied guilds for the season. All it will do is reduce the desire to deploy SCs, reduce the hits per day for players who enjoy GbG, and tick off those who enjoy GbG as it is now or are using GbG to quickly grow their cities. Thus there will be a new exodus of players and resentment from those who remain will darken the future for the game as new players will be be "poisoned by the griping from the veterans." Think that's not a thing, then consider why so many players sit in FE or before for years. This has happened in several games I've played in over the years and is akin to the "New Game Enhancements" of Star Wars Galaxies... and the story was the same in all those games - they never recovered.
Personally I think the answer lies in removing ALL the GbG buildings as they are what made it about guild treasury and diamonds and not about guilds just having a good all out war with each other. Granted it would be all about number of guild members and the percentage of which are active and the amount of their attack boosts....but really shouldn't that matter more than the ability of the guild to provide "free hits and mega rewards" to players with minimal attack boost? Don't get me wrong, multiple guilds could still work together, but they'd attrition out so quickly that at some point in the day smaller guilds would be able to come out and do some damage until the next day.
Regardless, too late and too much of a pendulum swing. Gonna bash a bunch of heads and make a bunch of enemies all in one update.