The Wii U is obviously 'revealed', but since July there have been nearly weekly rumors about X720 / Loop / Xbox Ten and also quite a few rumors regarding PS4. In July and August both were rumored to be at E3 2012, and supposedly there were super-behind closed door talks at Leipzig
I've previously outlined my take on when each platform would arrive based on software sales trends:
Wii U - mid 2012 in Japan, late 2012 in the West
X720 - late 2012 globally
PS4 - late 2012 to late 2013 - depending on how much money Sony has.
I've actually done a fair amount of research on leaks---> launch timing and typically you have an 18 month spread:
GC: E3 1999 to Sept 2001 (27 months from announcement, 15 months from real details in 2000)
PS2: E3 1998 (to combat DC) to March 2000
Xbox: E3 2000 to Nov 2001
Wii: E3 2005 to Nov 2006, although there were hints in late 2004
PS3: E3 2005 to Nov 2006
X360: E3 2004 hints to Nov 2005
3DS: April 2010 to Feb 2011
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu