Flashbacks between the past (SkyNet's development) to the current day (Judgement Day, war, nuclear threat, etc etc) would be something I would like to see.
It would be interesting to see some of the minds that went in to developing / writing the programme for SkyNet. It wasn’t all just about Miles D and what Cyberdyne were trying to develop.
Maybe in showing these clips of the past when SkyNet was being developed a clue could be unravelled that can be used in the present day to stop SkyNet, sort of like the developers installing a “back door” to the SkyNet programme. Just they never got to use it because of the immediate attack that prevailed when SkyNet became self aware.
And to fit in with Terminator coincidents, it could be that some of the SkyNet developers are still alive and out there, in hiding, or maybe in big bad JC’s army...