Actual size of the motor isnt really a big issue. Hartge managed to fit a v10 under the hood of an e90 bmw. Many cars roll with inline 6s which are theoretically the same length of v12s. And a w16 is similar to 2 v8s next to eachother sharing a crankshaft.
Along with the size of the motor, you have to consider the amount of weight you would be adding, which would not only make the car handle horribly, but be murder on bushings and other parts.
Point I was trying to make is cars are popular cool because they are so different and represent so many different things about the people who drive them. Dont bash someones 6 cyl camaro because they didnt go for the big motor. And I forget who it was but you might be impressed with what 1.3L can do if its a rotary