With Season 3 a huge success for Netflix, it looks like the next batch of episodes may begin filming a lot faster than last time. Considering the cast is growing up so fast, it would make a lot of sense for the show to get back into production as soon as possible. And it seems like The Duffer Bros. already had a lot in mind for the next season. They've already stated that the next season would be moving outside of Hawkins to other locales. This is quite obvious with how the finale left off.
Today, Production Weekly listed Stranger Things Season 4 as going into production in this October. For huge fans of the show, this is really good news. Instead of having to wait a year and a half for what might be the final season, it looks like it could come much sooner, potentially next summer if we're lucky.
There are numerous threads that were open after the battle at Starcourt Mall. Steering clear of all spoilers, we might see several changes for characters as they're not all in the same location any more.