This interview was done a few days ago, but I was surprised to see that nobody did a thread on it. It had a few interesting tidbits of info, but here are some of the major points.
You can check out the rest of the interview in the links provided in the Source section.
- Rank X
- The amount of active players in Rank X is a bit more than the initial players who were S+ 10 and above. Though this number is stabilized as Rank X power is reset every month and people with low power ratings get demoted. They explain the reason for why more people are in rank X is because more S+'s are trying to aim for it.
- Music
- When designing the music they thought that time has moved on and the trends and style of music have changed. This is expressed by having different bands appear, but when version 3.0.0 came along they wanted to balance that with a band from the previous game appear with Chirpy Chips.
- Octolings (Non-Spoilers)
- They planned Octolings since the start of Splatoon 2's development. However they didn't want to have Octolings suddenly be playable without an explanation, and wanted to find a way that could both explain that, get the player to empathize with the Octos and Off the Hook, which became the result of Octo Expansion.
Source: Famitsu (translated by the Splatoon subreddit)