Thoughts on eyeline matches, TOS, and communicating romance to the viewer
Eyeline matches, very simply, are a cut from an actor looking off screen to some disconnected object that was not frame. The cut communicates that the person was looking at the object. Note, not all cutaway shots are eyeline matches. The geometry and framing of the shot impacts this in complicated ways---but needless to say, if you've seen anything with two actors in different frames talking back and forth, each of those cuts are eyeline matches.
In TOS, attraction is generally communicated by eyeline matching an observer (typically male, in TOS usually Kirk) to a (often panning) shot of a person (typically female). In TOS this technique is often combined with a Gaussian blur over the woman to really hammer home that we're seeing her through Kirk's eyes.
The impact of this edit is so strong that it totally overrides acting choices. For instance, in Elaan of Troysius, we get a very blatant camera panning shot up her body despite Shatner not acting particularly attracted to Elaan (compare his reactions to Edith, or Areel, or, as we'll discuss, Spock).
And the flip side here is that the absence of this also overrides acting choices. It's very hard to deny from a still frame of Kirk looking at Spock that Kirk is attracted to him. We've all seen the gifs, there is very little difference in the way Shatner acts opposite Collins (Edith Keeler) as he does Nimoy.
But there is a difference in the edit! We don't get a panning shot up Spock's body every time Kirk sweeps his eyes over him (one exception: The Motion Picture). We see Kirk being love lorn, but we don't experience it, and so the uncareful viewer does not intuit that Kirk is displaying attraction to Spock.
All this is to bring me to my point: imagine TOS, as-is, but every time Kirk looks at Spock like that there's a cut away shot of Nimoy with the Gaussian filter (maybe the soft strings, too). Just imagine how that would play. No other changes, just inserting those missing eyeline matches.
