The development is officially finished, don't expect any delays.
Mario + Rabbids Kingdom Battle became a huge hit when it was released in 2017, despite the weird idea of combining Mario and Rabbids in a strategy title inspired by Xcom. For some reason, it would take five years before we got a proper sequel, but on October 20 it's finally time... unless there are any delays, of course.
Fortunately, there is no risk of that happening, as the official Twitter account of the franchise has now confirmed that the game has gone gold - which means it is finished. Basically, expect Mario + Rabbids: Sparks of Hope to be released exclusively for Switch within a month from now, just as planned.