arguments in both directions...
using singluar noun for second level in .INFO extension can be seen as using the noun as an adjstective... which can work... like "Car.info" is info about cars.
using plural noun can be seen as a description of a site that offers a selection among multiple things... like "Cars.info"
for my two cents, singular works slightly better in this respect with .INFO extension than with .COM, but still highly dependent on context
best wishes