Ahoy, pirates! Thanks for playing this game that many of us love and cherish so much. As I've been in the alpha since March and am not in the PP, I know how frustrating it can be to not be able to play with the other cool kids. ;) However, getting invited to the pioneer program is on an as-needed basis. When Rare decides they need more pioneers we will see an announcement made, most likely by the Forum Queen herself @khaleesibot , and invites will be sent out. To be sure to not miss such an announcement, please follow her by viewing her profile and clicking the green plus sign by her picture. It's also noteworthy that these pioneers are not given extra time to play for the sake of extra time. They are there to test ideas before they are implemented for everyone else. This means they are, in essence, acting as volunteer QA. This means you need to give as much feedback as possible, report any and all bugs you find, and generally help and contribute to the community and Rare. Now while the main criteria to be invited are only known to Rare, this should be a good start. Definitely not by asking for it on the forums.

You can also take a look at these links for more info on pioneers:
https://www.seaofthieves.com/forum/topic/25338/the-forum-user-groups
https://www.seaofthieves.com/forum/topic/25337/information-on-the-pioneer-programme

Hope that helps you all out. Good day and Fair Seas to you all! :D