If James Cameron and his creative partners are still eager to keep the Terminator mythology going in a way that’s separate from the main canon, I would suggest moving to television, but given what happened with the taken-too-soon Terminator: The Sarah Connor Chronicles, that would also be risky.
Then again, given how much TV has changed in the right years since Sarah Connor Chronicles was cancelled, maybe a new Terminator show could find success on cable or a streaming service.
Giving the public a movie that’s echoes the original two Terminator movies rather than its follow-ups is the goal to strive for, and if/when that’s accomplished, leave this world of killer machines behind and don’t look back.
Whether or not that happens, the people working on Terminator 6 should divert their focus from setting up a new trilogy and use the talent they already have to conclude this cinematic series in the best way possible.