While I doubt we would ever get a full animal pack dedicated to rodents, there are still plenty of species that I think have scope to be added to Planet Zoo. These are seven I would love to see:
Capybara (South America: Aquatic, Grassland, Temperate, Tropical) - The most obvious of South America's rodents that is commonly kept all over the place; little more needs to be said about this one.
Eurasian beaver (Asia, Europe: Aquatic, Taiga, Temperate) - I would choose this one over the American species to celebrate the success of reintroductions that have sometimes been led by zoos; again little more needs to be said about this one.
Indian crested porcupine (Asia: Desert, Grassland, Temperate, Tropical) - I would take any species of crested porcupine but this one with its broad range of habitats from temperate woods in the Caucasus and Arabian deserts to Indian rainforests means it could have great application in many different exhibit types.
Madagascar giant rat (Africa: Desert, Temperate, Tropical) - An Endangered species endemic to Madagascar that is often kept mixed with lemurs in zoos; at 1.2kg in weight and 58cm long they are slightly bigger than the 900 gram and 53cm long meerkat.
Northern Luzon giant cloud rat (Asia: Temperate, Tropical) - Another surprisingly large rat, which can weigh over 2.5kg and reach over 75cm long; they live only in the Philippines and are becoming increasingly commonly-seen in zoos where they can often be kept in rainforest mixed enclosures.
South African springhare (Africa: Desert, Grassland) - Personally speaking, this is probably my most-wanted rodent in the game; they are quite large, often live in mixed enclosures with aardvarks and would provide a reuse for the hopping kangaroo rig.
Vancouver Island marmot (North America: Temperate) - A Critically Endangered species from North America whose survival seems to rely on a captive breeding programme being run by zoos; they are also one of the most strongly patterned and visually striking of the American marmots.
That isn't even getting into some of the other species high up on my list such as the Patagonian mara, any species of agouti and any species of tree squirrel.