Seems like she was being preserved and relocated, not to mention out of commission for a long time since she had no idea why McCree lost his arm. But who put her in the egg for so long? And why? And where were they sending her?
And what exactly is she, that she needs to be kept in a weird gas-filled egg transport like that? If she were a normal omnic I would think she wouldn’t require anything so elaborate. Strange.
She doesn’t seem to be a normal Omnic. She seems to be a former member of Overwatch and I believe was shut down because she was dangerous or something which is why they were transporting her like that.
Shes probanly a secret weapon to fight omnics in case of a new crisis.
We dont know if it was cryostasis, seems mccree had her core chip with him so its not like she would be active maybe she has a powerful internal core that can become unstable if her body heats up which it would in a place like where she was so cooling her body would keep her core stable
That makes more sense. Now that you mention core chip, it is odd now that I think of it that it seems to be removable, is it possible that there was more than one? Is her identity located in the chip (which McCree keeps with him) and the body itself is replaceable, so McCree wasn’t looking for her specifically but rather for a body that could host her? Or is the chip just like a key that activates the dormant mind/body?
Echo might not be an Omnic but God AI on the sides of humanity. AI might not have rights like omnics.
I get the feeling Echo is a literal Echo of someone that died and the omnic we see is one of many, the logo on the omnics head is similar to vishkar and the design of Echos body fits the design and style / color palet of vishkar
Might be that she is a part of Athena who is obviously a pretty much only remaning god A.I and thus her operating status was considered dangerous and illegal.
Athena is not a god AI, and Echo is not related to Athena.
From an interview on Eurogamer, Jeff Kaplan said:
In the old picture… Sometimes what an artist like Arnold does is say, ‘There’s too much white space, I want to put a logo on,’ so he just put the Athena logo on the model. And the community embraced that model as being Athena. Athena is actually Winston’s AI, which is a separate thing - this character is separate from being Athena. The players also know Athena as the narrator of the competitive matches as well. But this is Echo, who is somebody completely different.
He’s referring to an old image from early development that has what looks like Echo standing in the middle of it.
I think you’re referring to this picture?
And yeah, the logo on her head and waist does look to be Athena’s logo:
There was also the cut hero from the original Prometheus pitch named Iris (whom I guess may have later inspired “The Iris” that the omnic monks keep referring to):
Interestingly, it seems the Athena logo has appeared on other robots in the Overwatch universe, like with this robot on display at the museum in the first cinematic (whether it’s still canon or related to Echo, guess we’ll see):
It seems like all these different design elements evolved to eventually create Echo. How these elements influence the final version of the character I guess remains to be seen.
Riding as cargo is probably cheaper than riding Coach.
Just saying…
I have a feeling Echo’s version could possibly the same version. Echo in humanoid form can possibly be transformed into a quad-legged tank/gun form similar to Bastion transformations. 
Echo could be designed like Ditto in Pokemon. Maybe she can steal abilities.