I'm confident Alden would be a good fit for the part if they go with him. He certainly looks the part in those new desert shots.
I would definitely like to see future films focus on a younger Indy as we have the 1930s pretty much covered with Ford's first three films. I was also a big fan of the Young Indiana Jones show back in the day and that could certainly serve as a template.
While I liked the magical McGuffins (crystal skull not so much) in the films, I always felt Spielberg and Lucas missed a lot of great potential storytelling by not deviating from the formula. Jones and the era by themselves offered plenty of opportunity for awesome globetrotting adventure without having to have some hocus-pocus trope - which seems to me is a trap for filmmakers who become convinced that you have to stick to a specific formula. Indy as a spy on the eve of World War II or during the war could have been a great story by itself, for example.
That's where the old Young Indiana Jones show really did well and was able to stand by itself as a solid series apart from the films.
We all know, after all, that Indy first encountered magical McGuffins in Raiders, as he expressed serious scepticism about "superstitious hocus-pocus" at the time.
More on that here: http://raven.theraider.net/showthread.php?t=12947