I agree with Valtien and Miez that there should be some kind of egg sink. Non-legendary egg prices have plummeted, and legends may be soon to follow with the Patreon bonus.

Rather than a straight sellback for eggs, I prefer the idea of egg quests. Have any of you ever played a petsite called Rescreatu? It has eggs as well. There is a quest giver that asks for a certain type of egg. His quests come one at a time and are unique to each user. Also, they don't have an expiration time, so you can do them at your leisure, especially if you need to bid on or hunt for a specific type of egg. When you are able to bring him one, you get points to use in his special shop, which is filled with items exclusively available from him (including an exclusive egg!).

Actually, if I recall correctly, Rescreatu's quest giver doesn't ask for an egg but instead asks for a specific color of a specific pet (in Pixpet's case, it would be something like "rose Troffinch" rather than just "Troffinch egg"). This could be another way to have a pet sink and would encourage users to hatch their eggs to try to hunt for that specific color. However, it would really need to come with a way to sell or trade pets themselves, or else it is easy for people to get stuck on a quest for a very long time.