He was on Jay Leno last night....and Jay asked him if we were ever gonna see Indy Jones 4, and Harrison thought for a moment and then just said "Yes. Uhhhhhh....it's on the front burner...".
And I heard on the 2nd Stern show a clip of George Lucas where he said his immediate focus was Indiana Jones.
I wanna see the Road Warrior film "Fury Road", but I am not sure Mel Gibson will decide to do it. At one point an announcement was made that they were working on a good script, and then I heard nothing....
http://www.starseeker.com/films/madmax4.htm