I just had an idea for a 50th anniversary 4-parter.
I don't know how much longer Matt Smith plans on hanging around but just around 3 years seems to still be the Doctor average. 2013 would be his 4th season. What if they split up the season like they have this year, and Smith regenerates in the middle of it. Begin the season with a 11th/12th Doc crossover from 11's perspective, then end with the same story from 12's perspective.
I don't know how much longer Matt Smith plans on hanging around but just around 3 years seems to still be the Doctor average. 2013 would be his 4th season. What if they split up the season like they have this year, and Smith regenerates in the middle of it. Begin the season with a 11th/12th Doc crossover from 11's perspective, then end with the same story from 12's perspective.