Newbie theory... sorry if this is a duplicate of someone else proposal:
Soundbite version: The Discovery Universe is the (or a) predecessor to the TOS universe, the Red Angel is changing the past to eliminate AI corruptable tech that we don't see in the TOS or TNG.
So here are my thoughts; Discovery presents a tech evolution and a blend between Enterprise and TNG/DS9, but TOS is so away from the tech seen in all three, and the holo comms really don’t show up until late in DS9, and then don’t quite work quite right.
So, what if, just like the Eugenics wars, the Federation becomes ultra paranoid about advanced computers systems after this season of Discovery or the Red Angel resets the timeline in such a way tech is not allowed to evolve.
Control is defeated at the end of Season two and the Federation outlaws all cybernetics and “WIDGET” technology that lead to the creation of ‘Control’, pushing the deployment and use of older, non-intelligent Duotronics from Daystrom. This would explain why Starships in TOS have so many people doing all sorts of manual things better accomplished by automated systems, and why tricorders are less capable than the phones we have in our hands today. All of this kind of tech and these systems that have been eliminated or outlawed because of the risk of another ‘Control’.
It's a major step back for the Federation, and the others (Klingons, Romulans, etc) take the same step back for fear of the same happening to them.
Also, as part of the 'Control' backlash, Section 31 is disbanded and/or disavowed, but not really, as they drop off the grid after Season two of Discovery (maybe the basis for the Georgiou centric show in the works; who else to lead S39 than a person from another universe with mirror morals). This can explain why no-one has ever heard of S39 when they pop-up on DS9.
Who’s the Red Angel could be anyone, including Spock’s Mother for all we know. She would know and trust Spock more than anyone. It could also be Airiam from another timeline, one where she lived, and then survived the destruction of all organic life; mostly because she was only part organic. If it's her, she working behind control's back from a future timeline that will cease to exist when everything is reset... again.
If you really think about it... this all ties back to the Time-War that was happening in Enterprise, could be part of that conflict spilling over into adjacent timelines, or as I stated above; STD could be the predecessor to the TOS universe as the Kelvin Universe was spawned by TNG Spock and a Romulan Supernova.
This whole multi-mega-verse, I'm tired of this cannon, let's create new cannon, is getting tiresome. I feel like we're dealing with DC and Marvel trying to recon their various reboots into one universe. Just start the show by telling us, "A long time from now, In a universe next door..."
A couple of more things; Michael must die if TOS, as we know it, is to happen. At least she needs to escape the destruction of the STD universe and end up in a TOS Universe where Spock’s adopted sister died and that Universe's Spock never met, or meets, Michael from the STD universe.
And, don’t forget the STD Short where we find the Discovery waiting at the edge of the galaxy for a recall message from its captain (Tilly?). We don’t know if this is the future or the past, but it’s a good platform for time travel, or for a message in a bottle kind of thing that might show up in the Picard Series. And, if it is the platform for the Red Angel, I can't seem one person doing all of this alone; the Red Angel has to have some sort of support we're not seeing.
Too much?
