Channel Hop: How the producers got away with a lot of the season's Family-Unfriendly Violence. They told the first network (Fox) that Cole's parents would've later turned out to be alive. They then "neglected" to tell the second network (Disney) that the death had ever happened, so they didn't have to keep the promise, and they stayed dead.
Executive Meddling: Apparently, Forever Red was going to be a two-part episode that would have ended with the rangers summoning their respective megazords and taking down Serpentera together. Disney however did not like the idea of spending money to create the CG zord footage as they didn't have toys to promote and told them to cut it into one episode as the team-up was just expensive in general.
More meddling came from Bandai, the company that produces Power Ranger toys. After Disney refused to fund Forever Red, the writers asked Bandai for money. They agreed, but only if the episode promoted the Wild Force Rider toy, which is why Serpentera, Lord Zedd's most powerful super weapon, gets taken out by a motorcycle...
One of the Mutorgs from "Reinforcements From The Future" was Deviot's monster form from Power Rangers Lost Galaxy recolored. (They were originally going to use the Orgs from the Gaoranger movie, but they were lost in a fire.)
There are officially 100 Power Animals, but we only ever see 22. Toei actually designed and detailed about a dozen more exclusively for Wild Force, including a peacock with many weapons as its tail feathers and a wallaby with a baby in its pouch. These can be found in the artbook Super Sentai Robot Art Collection.
Forever Red was originally going to be two parts, though it was forced to become only one part thanks to the fact that another crossover, Reinforcements From the Future, happened recently, not to mention that it was two parts long. Many things were cut out of Forever Red, most notably the original fight with Serpentera.
Much of the Ship Tease in this season was supposed to have an actual payoff, with Danny going back to the flower shop with Kendall and Cole and Alyssa being married in a Distant Finale.
In addition to Cole's parents being brought back to life, another idea was that the attack by Master Org that "killed" them actually brainwashed them into become Jindrax and Toxica.
According to the Ranger Wiki, Kendall was going to become a ranger at some point. It's unknown if she was going to be an American exclusive ranger, or a replacement ranger though.
The teaser for this season shown after "The End of Time, Pt. 3" showcased an opening theme completely different from the final, presumably not used due to rights issues from the Power Rangers franchise's sale to Disney.