^Wait, isn't Salvation the movie during the war?
Yeah it is but it's set after the events of Terminator 3, so it's technically not the war we all wanted to see (The one set in either the Terminator 1 or Terminator 2 timeline.) but close enough. Still found it weird John didn't act on that machines can learn and detach themselves from Skynet's programming which could make them good allies for the Resistance.
Wouldn't future John instantly know if it worked or not the moment Kyle went back in time? T1's goal was to protect Sarah, and since John still exists the moment he sent Kyle back he knows it worked out - though he does not know that Kyle is his father. Kyle being sent back was a reaction to learning that a Terminator was to be sent back.
Well we don't know how time exactly works in Terminator, does it splinter off and create a new timeline? (According to the trailer for Genisys, it does.) or does it just reset and causes the changes in time effect the whole timeline (SPOILER FOR GENISYS:
According to the leaked script, yes it does.) when one film has both theories, it's hard to say how it actually works.
Besides even if future John knows that sending Kyle back in time worked, If we followed that timeline Judgement Day still occured but that can't be because in the timeline of the movies, the second time Arnold was sent back he managed to stop Judgement Day. So from the looks of things in Cameron's original films, time only changes when someone actually goes back in time and changes the whole timeline, there is always a maximum present until it is changed and... Well, I'll let the Doctor explain;
https://www.youtube.com/watch?v=vY_Ry8J_jdw