I just hope the books are out before the show does catch up. Realistically, 2014 for The Winds of Winter and then he has to give us the ending of the series and give us the final book in 2017. Unless of course....he needs more books to finish the series.
Season 1 - 2011 A Game of Thrones
Season 2 - 2012 A Clash of Kings
Season 3 - 2013 A Storm of Swords 1
Season 4 - 2014 A Storm of Swords 2
Season 5 - 2015 A Feast for Crows
Season 6 - 2016 A Dance with Dragons
Season 7 - 2017 The Winds of Winter
Season 8 - 2018 'A Time for Wolves' aka the inferior 'A Dream of Spring'
The show can not possibly expand Feast and Dance into more than a single season each.
P.S.