Whilst I'd love it to be a V4, the development cost alone would probably prohibit it just for this car. In addition, the layout has several shortcomings that basically amount to most of the drawbacks of the boxer configuration with little of the benefit. Which means no manufacturer would likely consider it for mass production and multiple uses.
However, the same could be said for the parallel twin in the Fiats, and the currently favoured layout of V4s in motorcycles for sports touring would probably have similar low-speed roughness (firing intervals), but much less vibration (inertial; reciprocating / rotating balance) compared with the twin.
But the twin is a smaller engine, smaller capacity; if you need four cylinders, and have space for a V6, an inline four is probably the easiest and best option.
There are a few things they can do to tjuzs it up a bit, to give it a bit more character in the historic Alpine fashion; inline fours needn't be insipid.