The model I presented earlier weirdly works if you take into consideration that Sakurai has said characters typically take 10 months to a year to complete.
-Plant, Joker, Hero and Banjo are all being worked on in December.
-Plant releases super early February. Terry probably began development around this time. Late January/early February to early November would be roughly 10 months.
-Joker releases in April. Blythe potentially begins development around this time. Again, the timeline fits if we assume Blythe started when Joker was wrapping up. Late March/early April to late January/early February is about 10 months.
Let's now go in reverse.
-DLC was supposedly first pitched to Sakurai around March 2018, green lit around E3 2018, and finalized November 2018.
-This model suggests that Joker probably began development around E3 2018, coincidentally about 10 months before his April 2019 release.
-The Seven Squares memo happens sometime in July 2018 and is leaked to the public in August. This suggests that Hero was probably greenlit around this time. Again, it fits the 10 months to a year timeframe. Coincidentally, the big ass Smash Direct happened around this time too.
-Banjo was supposedly negotiated around E3 2018 and Papagenos heard about him in October 2018. We know that Banjo was already in development at this point so when approximately did he begin? Probably September and, once again, likely in a similar timeframe to not only the Fall Direct but Isabelle's reveal too. Fits the theoretical timeframe.