This seems fair only if...No, his first emote was already paired with the action of ENTERING. If you emote your arrival and in that same emote you're turning around to leave, it seems like you're doing two actions and should wait for someone to react.
This is upheld, because otherwise you'll get player A who will butt themselves before the entering player with a 'I approach you'. The entering player then takes their turn emoting an entrance. Then player A can go... 'And now I attack, lulz'. Other than that, I like what I'm hearing and I've seen it used to great enjoyment! The problem is enforcing it on everyone, and especially trusting others to uphold it. The latter is where I often fall short, and if there were some hard rules around these things I would definitely feel safer during these scenes. Well, maybe not safer, but y'know.1) We should not ever react to a character's entry, or consider them there for RP purposes, until they have posed in. This makes sense in so many ways: you don't know the state in which somebody is entering a room to respond to them, for example. This also ensures that in tense situations like this, you would have gotten a say.
On the other things (I.E. far away definition, and chase mechanic) I think that taking a step (maybe two?) should be a minor action. One you can pair with a major action like attacking. Anything beyond that and you'd be taking your full turn to move there, IMO. The upside being that if you use a full turn to move you can pretty much move anywhere that is uncontested (if I'm not actively pushing you away from it, guarding it, etc, you can probably move there).
As for the chase mechanic... well, to refresh:
I think that if nobody can actively stop me from leaving a room, I should be able to. Unless somebody is right beside me when I enter, they shouldn't be able to both move to me and attempt stop me before I can turn around and leave (provided I don't dawdle). However right now, after escaping a tense scene, I spam my way to a safety. This shouldn't be how it is, I know, but mediating a chase scene is something that is currently beyond players without knowing each others stats, rolling dice, etc. Most players aren't willing to account for variables like crowds, fruit carts to hide behind, things thrown behind, etc - and I -will- use all those things to my advantage, you bet your ass.3) We need an official mechanic for "can I leave the room before you catch me" that doesn't depend on "can you somehow code-attack me before my 30-sec walking out the room thread completes." Like guard, but one that doesn't assume you're already there - one that assumes you're running to try and catch them.
But a straight across chase via code just seems like a game of whoever runs out of MV first, and that's just stupid. It will be whoever has the most magical porkchops wins.
So, if you could code a chase mechanic in, how would it work - or how would you mediate a chase scene assuming that 'villain' did escape the room but 'hero' is still hot after their trail?