While there are all sorts of fun and deep-cut guesses, when I go with my gut and base it on how they seem to hand out surprises that in the end aren't *that* surprising, my mind goes to Michael Burnham. Though the theory above about Amanda is compelling, and would fit with the tone of this season.
Fuller he worked on the series concept, Changing the Klingons for no reason, Said that there'd be no round nacelles, Fans could feel their stomachs a-queasin'. A brand new Trek can give you a heart attack-TACK-TACK-TACK-TACK-TACK, You oughtta know by now...
It's probably too early for the Cardassians to turn up (even though we don't know when first contact took place), but if not...maybe the Red Angel could be: (puts on sunglasses) ...an Uptown Gul. YEEEEEEEEEAAAAAAAAHHHHH!!!!
To all those who think the Red Angel is future-Burnham: I don't agree. Surely Spock would have sensed her during the mind meld? What you had to do. What you always do. Turn Billy Joel puns into a fighting chance to live.
Re: the Red Angel... [saddestmoon awkwardly takes Mic] ‘...she can wait if she wants/ She’s ahead of her time! It’s like poetry...
The Red Angel is Ilia. She represents V'Ger, who'll reach out to Spock again, 15 years later... ... no it's not. But it randomly popped into my head just now.
I think there is a purpose. We just don't know what it is right now. It's revealed itself to be noticed and to be associated with good interventions. It's planting that idea that Spock and friends need to follow it to save the galaxy. If it remained unseen, it would be hard to do its bidding! I'm guessing that later in the season, the RA makes a big ask, purportedly to save the galaxy, and it'll need to be a be known entity to do that.