This is one of the last casting choices I'd expect, since Jamie Foxx's Electro was probably the worst-regarded villain in any Spider-Man movie. That was more due to the script than his performance.
If Amazing Spider-Man 2 had never come out, we'd probably look at Foxx as an understandable and unremarkable choice for the bad guy.
My guess is they're using the character to seed the multiverse, but that it'll be a twist later in the film that this Electro has come from a different world, and already fought Spider-Man.
It is interesting how meta the casting choices for bad guys have been.
The 1980s Batman is hired to play the Vulture (after some earlier speculation.)
https://www.vulture.com/2015/09/emma...n-trailer.html
Jake Gyllenhal was rumored to replace Tobey Maguire in Spider-Man 2, and they bring him on as Spider-Man's mentor in Far From Home.