SPL and SFL clubs backed the controversial proposals for league reconstruction last month.
And Doncaster expects both groups to approve the move to a 12-12-18 structure when they meet again in March.
The plans, which will see the top two divisions split into three after 22 games, have been widely derided by supporters across the board.
However, Doncaster stressed that a 16-team league was "financially unaffordable" and that there was not enough support for a 14-team top league.
He said: "Fans tell us they want a single merged league, an all-through and more equitable distribution model, play-offs, a pyramid structure, significantly more relegation and promotion, and more meaningful games.
"The only way we can achieve that is through consensus and we are only going to get that through this model.
"If people want these changes that everyone says they want, we need consensus and the vast majority of the 42 clubs to vote in favour of the package.
"There were some clubs that would perhaps want a bigger league. But they know we need consensus.
"If you put a 14-team model on the table you're not going to get that."
He added: "There will be far more meaningful games that fans want to go to.
"What it will give you is real tension in the second half of the season.
"Every club in the middle eight has 14 games to determine their future."