Good question. 5e rules say EKs "commit [spells] to memory instead of keeping them in a spellbook" but also says they "learn your spells through study and memorization"
According to the rules then, it seems like they should be able to learn more spells this way, but their limit would still be their memory: i.e., they couldn't increase the total number of spells they know.
The effect of this would be to bypass the "adjuration/evocation" restrictions on spells known, replacing an adjuration/evocation spell with whatever spell was on the scroll.??
That seems decently balanced