Yeah, that was originally a post on Reddit a few days ago. It has some good points, but it is ultimately a very, very flawed idea. For example, all the birds will be 1500 CP - it's already known that they have maximum CPs and since the idea only allows for the capture of one bird, how are they supposed to be powered up? Also, why should a level 2 trainer receive the same CP Pokemon as a level 30 trainer? By the time you reach level 30 any Pokemon below 2000 CP will be almost useless anyway.
Personally, I think birds should be released on a reward-based system. For example, only those that have captured 100+ unique Pokemon will be able to catch the legendary bird of their team. Once this threshold is reached, Willow speaks to the trainer and tells them of a mysterious new Pokemon nearby and asks them to investigate. He also hands them a Master Ball in order to capture this new Pokemon. The legendary bird will then appear when the player has walked 25km after speaking to Willow (with a little progress bar in the top left corner of the screen perhaps) and can be caught instantly with the MB. A system like this would ensure that only those that have caught a significant amount of Pokemon can catch the bird, while also making it very easy to catch once prompted.
I am unsure how the CP would work, as it would be unfair for higher level players to get a better legendary bird without the ability to power it up. Perhaps the CP of the bird is directly correlated to your level and each time you level up, you gain 10 Moltres/Articuno/Zapdos candy? That could work quite well.
Of course, IVs are gonna be a major pain when it comes to the birds. RIP to anybody who gets a 1% legendary bird
.