Basically this was supposedly written by a hired writer (David Wilson anyone?) simultaneously as the other team (Sarafian, Brancato, Ferris) worked on T3s script, as was the case around 1998-2000 ish and was supposed to be filmed back to back with T3.
Then when t3 came out they completely stopped talking about 4.
After, the writers of T3 have a script theyve presented to Kassar and Vanja. They intended to make the film without Arnold, with Mostow helming.
Then I guess those producers realized theyd actually have to work to get a Arnold-less T4 to work, so they sold the rights, to light their cigars, to Halcyon. Halcyon bought the script as is (WHY!? lol) and boasted theyd try to reinvent the franchise as a future war franchise about General Connor.
Now, Halcyon is in a legal battle with MGM who made T3, saying that they were supposed to see who tf was casted in the film before the agreement, because they want to make sure their merchandising clause in the deal makes the most money you see. Now its in development hell pending the case.