In no particular order here's what to expect. Some have already been announced.
GElv6-10
GbG with blue stat fighting
Auto troop refill - when a player sets the troop formations the game will automatically replace killed and injured troops of the same type after the battle is complete. For 2 wave fights it will auto refill after the second wave but not before.
Production quests will migrate to same age. Starting with the Summer Event Rival quests FoE will exclusively use productions of the same age. This change will not be immediate and for all game mechanics. For example the Summer Event quests will have what we're used to now. Eventually we will no longer be able to put a bunch of blacksmiths down for events so best to get the pumpkins now.
GB's are getting a makeover. We have seen settlement buildings get an upgrade that transformed them from store items to the best buildings to have in a city. The GB changes will not be as big. They are a slight improvement. This is an acknowledgement from Inno that power creep has rendered most GB obsolete and they're course correcting. The plan was to start with the worst buildings (Colosseum) and work their way up to the most popular GB's. One particular dev thinks it's funny to start with the Arc. The golden upgrade image has now been widely seen. He thinks it would be funny to offer the golden upgrade at level 250 and have that degrade over time back to 249. In my view there's no way this happens or at least it won't happen first despite the artwork being completed for this asset.
Heroes will be rolled out very soon. It's basically just a limited time boost that's then time-gated before you can use it again. If used wisely and plan QI accordingly the alternating red and blue boosts can help struggling players quite a lot. The full Hero features will not be rolled out until later so we're getting a narrow version at first.