Eggs are a fairly new resource at the moment but they have the problem of being of limited use. At some point all the pets will be maxed and eggs will be become useless outside of event quests.
Therefore I propose a new Godai Element upgrade that allows you, similar to keys, to spend eggs. It is not so important what the upgrade actually does but it would make sense to somehow buff pet effects.
Even before reaching the point of maxing all pets this change could also become interesting because it offers players another way of spending a resource, giving them more room for decision making. Right now it is very simple, you get an egg and you open it, maybe wait with that for an event but that's it.