Was it ever mentioned whether or not companions are the only romanceable characters? Or are there other non-companion NPC options?

It hasn't been mentioned officially. I'm inferring from exclusion that non-companions are not romanceable, but I haven't viewed any leaked footage to confirm this.

Well, considering Skyrim let you marry just about anyone off the street, I guess I find it hard to believe they'd limit it to about 6 options. Not that I'd want the quantity over quality stance that Skyrim had this time around, where every option had cookie-cutter dialogue. but I'd expect some sort of middle ground.

You know with over 100,000 lines of dialogue it's a reasonable request.

Right? I mean, not to say that Piper or Cait don't look good. They do. But a couple more options wouldn't hurt.