Recently, Sony released this documentary to honor Ayrton Senna's memories. After all, it's been 20 years since he only lives inside our memories, inspiring people to do good things and keep forward. Not only that, Gran Turismo released a section about Senna in their webpage and also annoucend a future DLC, that will be added for free in the game in a next update.
So far, we only know about one car, the Lotus 97T, driven by Ayrton in 1985.
Source: GTPlanet
P.S. This actually makes me really happy, and not only about the Senna's DLC, but about the partnership with Ayrton Senna's Institute. By doing such thing, Gran Turismo will now help children in my country! A racing game never had so much respect from me. :lol: