In most markets, sedans are in decreasing demand and the popularity of SUV/CUV vehicles is increasing. By that, the Y should be in larger demand than the 3.
Also, the Y addresses some of the tradeoffs made for efficiency on the Model 3: the missing hatch and the low second row. The Model Y will have a proper hatch, more cargo space, more vertical space in row 2 and optionally even a 3rd row of seats, increasing the attractivity for families with many children.
Putting that together, there is a lot of reason to assume the demand for the Model Y might eclipse the one for the Model 3.