Whereas research acknowledges the potential of business model innovation (BMI) to destabilize an existing regime, the impact of a socio-technical system in transition on BMI remains under-conceptualized. To advance work in this direction, this study expands the concept of a business model design space (BMDS), which describes the opportunities and constraints to design novel ways of creating and capturing value from niche technologies available at a given point in time in a transition. Illustrated with the case of electric vehicles in the Netherlands, we show how BMI are affected by and, in turn, affect this design space. We find that the policy and the science and technology dimensions of the socio-technical system form hard boundaries to the BMDS that niche actors cannot directly overcome via BMI. Yet, BMI can push the softer industry, market, and cultural boundaries of the BMDS by supporting niche expansion via coupling novel technologies to business models that (i) conform to the current regime, or that (ii) attempt to transform the regime. This paper offers an analytical framework that connects firm- and system-level to support the exploration of questions like how much novelty niche actors can introduce into a ST-system at specific points in a transition.