The Ju89 was a failed design; the reasons the RLM stated for the cancellation of the project were its high fuel consumption and underpowered engines.The only relation it had with the Ju89 was the wing and tail.
The Ju89 AFAIK did NOT have these problems, problems that resulted from the changing of everything but the tail and wings, which were not designed for the fuselage that they were mated to.
But don't forget that one element of the changes after Wever's death was a change back to a tactical support bombing capacity with pretensions to a strategic capacity...which led to several more years' institutional blindness regarding the NEED for a maritime recce aircraft.
You really can't...and shouldn't...get around the fact that NOONE in the RLM or Luftwaffe saw the need for anything in the class until 1939; because that meant that the Ju 89 was not going ANYWHERE in 1937. The militarised Ju 90 ONLY appeared much later because Junker's concept hung around long enough courtesy of the Ju 90 airliner project to meet wartime requirements coming the other way.
You shouldn't try to wave away these issues; whatever potential existed in the Ju 90 ONLY survived to be capitalised upon because Junkers kept the torch lit. And don't forget - even that wing and wing didn't survive into the militarised Ju 90. It got new wings as well as stonger landing gear, and changed fins. It was a progression well away from the Ju 89....that only happened because of the evolution of the Ju 90 project.
E.R. Hooton states that the winding-down of both projects to demonstrator status began in November 1935. That's eight months before his death.The order for 3 of each prototype was maintained until 1937 when the project itself was cancelled.
Its interpreted that his issuing of the Bomber A specs and lack of orders for more by the time of his death meant that he intended only to use those 6 aircraft as demonstrators, but as of the time of his death according to that book the halt order for development was only issued in July AFTER his death