"If the rumours are true, such a slow lens could negate the benefits of having a large sensor. For instance, the Leica Q3 combines a full format sensor and a 28 mm f/1.7 lens to achieve low-noise images in low-light situations and a shallow depth of field."
-well that's not correct, the sensor size doesn't only alter the depth of field, but also it's proportional spread, moving away from the focus plane, as well as the overall impression of the image, since the lens of this fuji, remains being a 35mm lens, yet with the field of view, of a 28mm lens on kb.
furthermore, the physical boundaries are shifted, f.e. in terms of resolution, or aberrations...
in other words- you can't call a 35mm lens on this mf, being an equivalent to a 28mm lens, neither in regard of aperture, nor in any othe and the differences regard mainly other parameters than low-light sensitivity ...