I said it before and I say it again:
We should have seen the Romulan War
IIRC, wasn't it stated in TOS that the Romulans had never been seen face-to-face before? This would make for some difficult, to say the least, writing for television. Unless we want to wipe the minds of all the Feds at the end of the war, or go back in time, or . . . .zzzzzzzz.
Well, it wouldn't have been a problem had they simply done away with visual communications (save between Earth Vessels) and stuck with audio only.
And then, you'd have a couple of ways of doing this ...
Going by the calendar (as I recall it) the last (7th) year of Enterprise would've been the opening rounds of the Romulan War, so there wouldn't be much face to face interaction anyway.
So, present them as a mysterious unseen enemy -- one whose depredations must be countered even before the good guys know who they are. And like any good mystery, you keep their identity secret until the final reveal of a Romulan War Bird.
The other way is to present both sides of the conflict (a la
Tora! Tora! Tora!) as the incidents begin to escalate through out the final season.
But then again, this is the problem with Prequels. All too often, people want to hurry to introduce and link to the familiar, rather than let events and the story unfold at its own pace.
/s/
Gloriosus
the G-man Himself