I think there's a very good chance they'll do something with the Earth/Romulan war in about 5 years' time (since the current 5 year plan for Trek is already mapped out it'll be the next phase). It's the one "big" event in Trek history that hasn't been explored in canon yet. And while the main cast has aged somewhat, they could always fudge the dates of the war itself (who really cares if they move it to 2175 or whatever? Was it ever spoken in dialogue or is it just the stuff of manuals and background graphics?) if they want to include them.
The dates have been established as being between 2156 and 2160, both in IAMD, pt 2 and "Balance of Terror." With the attack on Starbase One being the beginning and the Battle of Charon being the end. And both sides having atomic weaponry. And using radio communication only.
We also know that an Earth/Vulcan/Andoria/Tellarite alliance forms at some point during the war. And that Earth is capable of at least Warp 7 by the end of it, since Daedalus-class ships were the main ships of the 2160s.
We know that Captain Stiles served during the war. Whole families did, as least from Earth. As did MACOs.
Romulans were prideful, and would rather self destruct their ships that receive help. So I’d imagine the response is similar in regards to being captured.
And that the event is sometime called the Earth-Romulan War
s – suggesting there were numerous truces and ceasefires over the course of the conflict. Whether they were tactics to gain an advantage or genuine attempts are unknown.
We don’t know what from the
Star Trek: The Beginning script is true, aside from there being a Romulan attack on Earth, since DS9 established that did happen – although I can see Shran faking his death to work on the project stated in the script.
If its true that that there were ships using the USS prefix, then that mean there may have also been ships using HMS, VK, DEV, SS, DY and others (based off of known prefixes according to the TNG episode “Up The Long Ladder”) – suggesting various nations sent ships beyond a United Earth military response.
The various Pocket ENT relaunch novels suggest the Romulans attack Coridan, and that the Romulans are supposed to have a telecapture device that they used, to go along with their holographic technology from their drone ships. But its not canon.
Another book –
The Romulan Way, from 1987 - suggests that the Romulans were a pre-warp species and used primitive sublight vessels (the same description Spock used) to capture a ship to reverse engineer warp drive. This book is also not canon.
The videogame
Star Trek: Legacy suggests that the Romulans were supplied metagenic weapons from a Vulcan named T’Uerell to use against Earth colonies, to explain atomic weapons during the war. Even though "Balance of Terror" already established that the Romulan BoPs actually carried atomic weapons onboard. I don't think this video game is canon, since its a crossover with the other Trek series too.
There’s never been a denial that a Federation-Romulan cold war was underway. We just know that Section 31 predates the Prime Directive – which means covert operations would be happening against the Romulans anyways, even if the Federation denied they were happening. And that Archer serves as both an admiral (2160s) and ambassador to Andoria (2169 – one year after the Prime Directive is established), before serving in Federation politics and becoming its President for an eight year term starting in 2184. Meaning it's likely he okayed a number of S31 operations if he became aware of any of them.