Friday's announcement was thin on details of how closer convergence would be achieved. Relations between Renault and Nissan engineering teams have sometimes been fraught, hampering savings in areas such as engines and transmissions.
The strategy plan announcement disappointed analysts impatient for a new capital or management structure to speed integration and prepare Ghosn's succession.
There was "no answer from Ghosn on the possibility of a merger by 2022", Jeffries analyst Philippe Houchois noted.
Ghosn has been seeking a new second-in-command, sources told Reuters in June. But such plans are linked to thornier questions about the balance of power between the two main carmakers and the French government's outsize clout as Renault's biggest shareholder, supported by double voting rights.
Ghosn, 63, declined to stay whether he will stay as chairman of the alliance for the plan's entire six-year period. He stepped down as Nissan’s chief executive officer this year but continues to hold that title at Renault. Ghosn's current contract as Renault CEO expires next year.
Convergence efforts will continue with no radical change to management structures, Ghosn said.
"Six years is a very long period,” he said. "We are going to take it step by step."
More information on operational and product strategies and financial goals are expected when Renault, Nissan and Mitsubishi announce their midterm plans in the coming weeks -- starting with Renault on Oct. 6.
Bloomberg and Reuters contributed to this report