TL;DR: Only omnivores, plants, and some former carnivores will be left after a few years. There will be some ex-herbivores, but they will be relatively rare.
If the plants become carnivores, here is the progression of events:
(1) Previously non-carnivorous plants would consume most of the previously carnivorous plants like Venus Flytraps and pitcher plants. Those that survive will die of malnutrition, since carnivorous plants are carnivorous due to a lack of available nutrients. Liverwort might survive, but that's about it.
(2) When the plants run out of other plants to eat, they will then consume most of the land-dwelling reptiles (snakes, anoles, geckos, etc), since they cannot easily avoid plants.
(3) All bacteria will die of malnutrition. Bacteria are, by default, carnivores; there is nothing else for them to eat.
(4) The vast majority of fauna will be caught unaware by the suddenly-hostile flora. As a result, most of the suddenly carnivorous plains and jungle herd animals will die. The former carnivores like lions will also suffer casualties, but they will probably suffer less due to their usage of caves and outcroppings as home bases. Mountain animals like goats and sheep will survive relatively unscathed for the same reason.
(5) The vast majority of the surviving ex-carnivores will now die of starvation. While herbivores can eat animals easily, the same does not go for carnivores. A lion can eat fruit and nuts in a pinch, but otherwise unable to process plant matter. Even if the spell does change their gastric tracts to be compatible, the will still not be able to get enough sustenance; most plants simply do not provide enough nutrients. A few will survive, but, weakened by hunger, the vast majority will be killed by former herbivores.
(6) Due to competition among the suddenly-carnivorous plants, the rainforests will become barren wastelands, devoid of life. Those plants which remain will straggly, and thus not worth eating. Chances are, the rainforests will eventually become deserts.
(7) Humanity will probably die. To be blunt, we are a very specialized species; without modern technology we would be unable to cope. If modern technology is allowed, then we would probably survive; after all, we have developed weapons specifically for killing plants. Seriously, the 20th century made plant-killing into an art.
(8) The end result will be that the world will primarily be dominated by pigs (those things are invasive even in their home environments), plants, and maybe humanity if we have a high enough tech level.