NBC would have put it in an even WORSE time slot?
Yeah, but that doesn't mean we can't see them onscreen, it just means humans never meet them face-to-face or have any visual communication with them. They can always be shown on screen, because everyone who knows even a little bit about Star Trek knows what the Romulans are.
Possibly. Vulcans seem to be pretty secretive about some things they find embarassing.
That might work well. Maybe humans even assume the Romulans look something like remans -- which would make the revelation that they're offshoots of Vulcans even more surprising to them.
"Balance of Terror", the first appearance of Romulans in Trek, established that Romulans didn't have warp drive. However, since that detail makes no sense whatsoever, it should be more or less ignored. On the other hand, since Romulan warp tech is quite different than what most speices seem to use, maybe humans make an erroneus assunmption romulans don't have warp drives.
And they should probably bump off a couple of characters named Stiles.