Regardless of how much the GbG farmers desperately try to doomsday cancel the rebalance, I'm sure the impact will be significantly less grim from a more objective point of view:
1.) FoE is an exceedingly good product for Inno, unrivalled even. It's highly unlikely that a major part of the revenue is made from diamond GbG farmers, if they're been outmatched by the real competitive top, it's probably hardly gonna chance a thing to the revenue.
Prove of the great performance of FoE was find by another player and published in
this post
2.) 1,X boosts pre-existed from the GbG-farming exploits, they where running perfectly fine in profits made from GB sniping, profitable boosts, etc. using fps from virtually unlimited fps and massively large fp-producing cities the availability of fps remain enormous. The strong pull due to the benefits from 1,X boosts remain the same and as said the large fp reserves ain't going anywhere. Thus making the impact from GbG-farmers' harvests taking a hit very limited
3.) Regardless of this rebalance, the real competitive guilds will remain on top. Not motivated by GbG harvests they'll continue to dominate in 1kD like business as usual. Perhaps with a little more effort none the less they will remain competitive. Much as any other guild motivated by competitiveness rather then profitability for lone wolves in their guild.
4.) A exodus event might happen at a limited scale by the angry GbG farmers who see their "farm" yielding less "harvest." This will be fine but difficult to measure as a regular player. I'm sure Inno has the tools to their disposal to measure this and making the right decisions. As said before GbG farmers may leave but they've probably not spend real money in the game anyways as GbG farming provides them with the diamonds to fund their farming frenzy.
5.) Weak guilds won't be hit. Weak guilds can't afford SC and if they can and managed to get into the top, they've been in the wrong league. Nothing would really change for them, the strong will always be stronger and beating them.
6.) In the end there's probably hardly anything gonna change besides the real competitive top guilds claiming their thrown, af the expense of the phantom "top" guilds who only survive in SC. This is also likely true for GbG farmers. Which they probably correctly see coming and why they try to turn this topic into a echo chamber. In the end from an player's perspective it's impossible to know for sure what the impact will be the grand scale of things, only Inno has acces to the tools and knowledge for this.
As an player we all suffer from confirmation bias as all we know and experience is how we play with like minded people. If we don't like something that might make us quit, our guildies likely feel the same, assuming this to be the "majority" is just a dangerous assumption. Not being able to understanding this and taking it into account, is just leading to discussions like this: emotional and self motivated bias discussions with speculations assumed to be the truth and facts.