Codemasters said they were looking at it, and that it was something they'd like to incorporate, but they found licencing individual cars was very difficult. With just 20 days until the game is released, it's unlikely they will be included.
The FIA and FOM do not hold the licence for an "era". The teams hold the licences for their own cars, but the licence to produce the 2011 game is made with FOM. That licence is what restricts Codemasters from venturing out from the current season.