I'd rather see Cartoon Network in the parks, but I get why people want to see Nickelodeon. The potential is immense with all of the properties, and Spongebob is one of the most iconic cartoons ever made.
The only major problem I have with Nickelodeon is the fact that two other parks currently use the IP in the United States, including one super close to NYC. That could cause tons of marketing problems, and the land wouldn't be as unique as I would want it to be.