Conservatives have long planned to cut the number of MPs from 650 to 600, with reforms expected to come into place before the next election.
However, analysis has suggested after a surge in support for Labour at last month's General Election, Johnson could be ousted in the new seat of Hillingdon and Uxbridge, despite growing speculation he could become the next Tory leader.
Using votes cast in the election and proposals for new constituencies, research from website Electoral Calculus predicts that Labour could win the seats of both Johnson and Duncan Smith, with an estimated majority of 1,000 in both cases.
Prime Minister Theresa May committed to the Boundary Review in the 2017 election manifesto, but it remains unclear if it will proceed if the Tories enter into a "confidence and supply" deal with the Northern Irish Democratic Unionist Party.
The DUP will be among the most severely hit by the plans in their current form.
Three of their total 10 MPs are predicted to lose seats thanks to the changes, while a fourth DUP constituency, Belfast South, will disappear altogether.
MPs whose seats are scrapped will be subject to their own party's rules on whether or not they can seek re-selection for another constituency.
The initial boundary review proposals were published last September, and remain subject to further amendments. Notably, the redrafted proposals must also be passed by parliament.