Will they ever have an episode somewhere in the future that would bring back the Tenth Doctor and have him and the Eleventh spend time together like the old Doctor Who used to do with some of the Doctors there? Imagine the scenes between them with the Tenth having some criticisms about his new self and the Ninth feeling like he is being judged by his father. Amy and Rory would be uncomfortably stuck in between the conflicting Doctors while contrasting and comparing the two men.
Nine is Pretty unlikely at this point, but, even Tom Baker (#4) regrets missing
The Five Doctors now, and is doing Audio Plays finally, so, you never know.
At least 2 of the 3 Multi-Doctor episodes were Anniversary Specials, and Doctor Who turns 50 in 2013 (November 19, I believe?), so, there's a fair possibility Sylvester McCoy (#7), Paul McGann(#8), and David Tennant (#10), and maybe even Peter Davison (#5) all could make a return to Doctor Who TV in 2013.
#6 and #4 have changed considerably as they've aged, so it may be difficult to work them in, since they haven't been seen on Doctor Who for all these years.
#1 - 3 have all passed away (Including the Stand-in #1 played by Richard Hurndall in The Five Doctors, I believe)
#9 has mentioned many times he's not receptive to coming back, implying under any circumstances (he may give in, in a year, or maybe not for 55 years, it took Tom Baker a good long while)