Yes, you can still book a future cruise with Carnival, but you can no longer book a future cruise certificate. The difference is that with a future cruise, you have to select a specific cruise and with a future cruise certificate you don't - you can wait to decide at a later date.
If you know exactly what you want, then it's still a good deal - you just don't have the flexibility that a future cruise certificate offers.
47 Cruises & Counting! Favorites: Paul Gauguin to Tahiti: Uniworld River Cruises in Europe; any of the Celebrity Solstice-class ships; Holland America for 12-nights in the Baltics & Russia; RCCL for 14-night Greek Isles, Turkey, & Croatia; Holland America for 14-day Alaska cruisetour; 10-night Canada/New England cruise; 21 days in Hawaii including a 7-night NCL cruise; Oceania for 25 days in Asia; & 3 months touring Europe by train. And many days spent in all-inclusive resorts!