Did a little research into what the other 5 tracks could be for Forza 6.
So far, all of the tracks from FM5 are returning, with Indianapolis getting a ribbon update. This leaves us with 17 environments with 64 layouts (from Badned's list on Forzacentral).
Also announced are Daytona, Rio, Brands Hatch and Watkins Glen. According badned once again,Brands Hatch will add two ribbons, Daytona will add two ribbons, Rio will add one ribbon (possible more though, usually the cover tracks have more than one ribbon) and Watkins Glen with two ribbons.
From this, we can see at this stage FM6 has 21 environments, with a minimum of 71 ribbons. So In order to reach the over 100 ribbons that they are claiming (source, from this twitch stream w/Brian Ekberg http://www.twitch.tv/expertzone_xbox/b/669656057,The remaining 5 tracks must have atleast 25ish+ ribbons (30 if we say Rio only has 1 layout, but I assume it will have reverse/short etc). Does this mean would could see the return of a track with a variety of ribbons like Fujimi or Camino Viejo/Iberion/Ladera? It looks more likely now atleast!
Also Brian said there will be over 80 showcase events in career mode... wow thats a lot!!!
Environments =/= Tracks.
You can have an environment that has an Oval and a drag strip that could be completely separate but both are ribbons.