A new report suggests that Guardians of the Galaxy 3 will begin filming in early 2019 in Atlanta with an eye for a May of 2020 release date. This seems to fall in line with the Marvel Cinematic Universe timeline, which will see the movie premiere a year after the still untitled Avengers 4. The third and final Guardians of the Galaxy movie is expected to help usher in the next phase of the MCU and may see the original crew down one person, depending on the events of Infinity War and Avengers 4. James Gunn has already confirmed a 2020 release date, but no other information has been released.
Guardians of the Galaxy Vol. 3 director James Gunn revealed over the summer that he had completed the first draft of the script, but he has yet to comment on the reported production start date. However, the director is a big user of social media, so we can probably expect a confirmation soon. Pinewood Studios in Atlanta might as well be renamed MCU studios, since it seems that they're always doing something there. The report also states that the crew has already shown up to begin preproduction.
The Guardians of the Galaxy movies all have complicated and time-consuming sets to build in addition to the pre-visualization work that has to go down before production can even start. A May 2020 release date for Guardians of the Galaxy 3 has already been speculated about, since the previous movie came out in May. May 1st seems like the most logical of the dates, but Marvel also has August 7th and November 6th open for untitled projects. So, Marvel could be going back for an August premiere, like the first Guardians of the Galaxy movie.
As far as what Guardians of the Galaxy Vol. 3 might be about, that's anyone's guess at this point in time. The future of the team will be decided after the conclusion of Avengers 4, which is still over a year away. We'll probably get some hints to who makes it out of the epic battle with Thanos alive from set pictures, but since Guardians movies are usually shot in studios, it may be a little tougher to gauge. Adam Warlock was teased at the end of Guardians of the Galaxy Vol. 2, but James Gunn has not confirmed that the character will show up in Vol.3.
An early 2019 production start for Guardians of the Galaxy Vol. 3 makes a lot of sense, since there's a lot of heavy lifting to be done in the pre and post-production process. James Gunn and crew will need plenty of time to flesh out the digital effects after filming wraps and an early 2019 production start guarantees plenty of time for a 2020 release date. Again, this has yet to be confirmed by Marvel or James Gunn and is an unconfirmed report at this time. You can read the original report via That Hashtag Show.