If you look at their website they have a teaser pick for the game.

http://www.lucidgames.co.uk/products/

The last entry in their procuts list "Road Opens 2013" pretty much can only be PGR5 since the developer is mostly made up by former Bizzare Creations employees.

While I'm hopefull I still remain cautious about it happening.

A PGR out of the gate would be a nice breather for Forza 5. Guaranteed million seller.

Well this website also thinks so:

http://www.vgleaks.com/rumor-pgr5-to-be-announced-on-21-may/

I couldn't think of another game that teaser pick could hint at.

already posted half a year or so ago in different threads.

as example this one

http://gamrconnect.vgchartz.com/thread.php?id=154475

and yes, i really hope it's true.

I still think Forza 5 will turn up sooner then later if Turn 10 doen't show anything on the 21st I'm sure it will make an appeareance at E3.