In a report from 2006[1] they prognosed a start of normal operations in 2017 with a delay of up to four years but also the possibility of finishing early by one year.

In 2012 they seemed confident to open in 2016, but I can't really find the reasoning for that. As far as I can see there were also cost considerations playing a part in the decision.

Edit: apparently a very difficult Dolostone section was less proplematic than anticipated (again, couldn't find an english source for this)

[1] (in three languages but no english, sorry): http://www.parlament.ch/r/mm/2007/Paginas/mm_2007-04-27_9519...