There is actually no rewards or long term benefits for hatching Pokemon Eggs in Pokemon Go. However, it would be fun if any rewards or long term benefits are given to the players as it will set a new goal for them.
They mentioned about introducing a reward called ‘Golden Egg’. The ‘Golden Egg’ will be awarded after hatching 500 Pokemon Eggs. The KM requirement, on the other hand would be between 12-15 KM, which will separate them from the other eggs.
Here are the three ideas:
Once the Golden Egg is successfully hatched, you can choose any non-legendary Pokemon with an immediate CP of 1500 and some nice IV stats. This new idea will definitely help the trainers fill their Pokedex with a special Pokemon, they had been looking for.
Another nice idea to reward the trainers without affecting the Pokedex would be to award them with 10000 EXP, 5 Incense and 5 Lures. To add to this, the trainer will be able to pick one particular biome out of each biome which will narrow down their hunt for a specific Pokemon in the egg. Source: Otakukart
The trainers who have hatched a Golden Egg can also be given an opportunity to fully relive any events they have missed. For example if the trainer has missed any public event like Halloween or Christmas, he or she should can pick any of the specific event and relive it for the full time period it was actually up for.