The Roost has been found in the datamines dating back to the first release of the game, but not Brewster himself. Just some coding, but in regards to actual "predictions," then there would be the bushes, diving, and Redd.
I feel like we won't be able to answer that question until next year when more updates have come out. So far we have just had bunny day, Reese and Cyrus' wedding, Redd, and diving (right? did I miss anything?). If I remember correctly, datamine didn't find any coding for Reese when the game first came out and thought she and Retail (from NL) wouldn't be in the game. They were sort of correct, but I don't think anyone predicted that Reese and Cyrus would be the main couple for wedding season based on datamine alone. As for Redd, I am pretty sure I remember reading someone did find something in the code that suggested Redd would be in NH. Lastly, I don't know if anyone tried to predict diving in NH from datamine. (I also could be wrong about some of this since I don't really follow datamines closely and just read them occasionally.)
Pascal was datamined, but Gullivarrr wasn't... I think it's to do with if they've got an amiibo or not, given at the moment there's a load of characters that aren't in the game yet but you can get posters of if you scan their amiibo... so their entries get updated in the BCSV for when they're added in future updates.
I'm also gonna give a link for the Discord server where the datamines were originally posted: https://discord.gg/acnh