Today at Xbox's E3 press conference, it (On top of a super cool brick built car, on stage) was revealed with a trailer that Forza Horizon 4, would be having LEGO Speed Champions content coming to it:
Everything is Awesome plays heavily in the trailer.
The mentioned trailer, started with "normal" cars racing around, running into LEGO Speed Champion cars with then "Everything is Awesome" starting to play with the world having LEGO stuff become apart of it as the trailer went. Also of note, the game will utilize the games destruction tech to work well with the LEGO systems nature.
The expansion will release this week on June 13th. The price is currently unknown.