Just to add onto what
Slender
talked about yesterday:
Notice how in Sakurai's launch tweet he doesn't mention Plant. What does this mean? At that point, Plant was likely "done" or "had gone platinum." For people not familiar with the slang, when it comes to came development, when a game "goes gold", this means it's ready for the final debugging and "polishing." Based on leaks from this time period, Plant was being debugged as early as August. When a game "goes platinum", this means that it's ready to ship. Obviously, game development isn't like turning in a homework assignment online and instantaneous. Sakurai doesn't work on a character until the night before its release and then slam the enter key at 11:55PM to make sure it releases on time. For games there's a cool down period of sorts where a developer makes sure things are in order so it releases smoothly. For physical copies, this is typically 3-4 months. For online content, it's usually about a month or two.
This is significant because this means that Plant "had gone platinum" in November/ December 2018, meaning Sakurai and his team were able to start the early stuff for Banjo. Looking at the Fighter's Pass, we see several points in time that seem to be solid indicators of when certain characters went Platinum. Joker likely hit this stage around the February 2019 Direct, Terry around the September 2019 Direct, and Byleth around Terry's November 2019 presentation. I think you all already see where I'm going with this.
Based on this model, if Byleth went platinum in November/December 2019, 8 probably began work around this time. Sound familiar? It should. If Joker, Hero, and Banjo were in development in December 2018 then 6, 7, and 8 were likely in development in December 2019. Now let's fast forward to March. Sakurai says that 6 has been delayed but flat out says that it's coming in June. What does this mean? Because 6's original release was supposed to be April, the original plan was likely to have 6 go platinum in February. Again, sound familiar? Based on these changes, 6 likely went platinum in April. This being said, 6 is "done" is just waiting for release at this point. With this in mind, Nintendo's likely actively working on 7, 8, and 9 at this point. Once again, this lines up with not only 2019 but 2015 where we wound up with three reveals at E3.
Going through all these steps, this seems to be intentional. If 6 hadn't been delayed, 6 would have released the same month as Mewtwo and Joker, setting the stage for at least two character reveals at E3. Think of it this way... If Joker hadn't gone platinum in February 2019, he would have been in the exact same place as 6 is now, likely being an E3 release like Lucas, Roy, and Ryu were. Again, this seems intentional and a very well structured work flow. In conclusion, E3 2020 probably will be 6, 7, and 8 unless 8 had complications we are totally unaware of because, as shown here, the "flow" is step by step near identical to how it was for the Fighter's Pass and even Smash 4's DLC.