The reason Indiana Jones could be played by someone else now is that there is a new generation of movie goers not familiar enough with the original IJ movies to have to need Harrison back again.
Indiana Jones is a character and Harry played him well and had the advantage of putting his stamp on the character. We were very close to having Tom Selleck as our beloved adventuring archaeologist and it would have worked in a slightly different way.
Our experience of having someone else play Indiana Jones is not going to be some insult to Harry's contributions, in fact it will be a damn good challenge to the next actor as Harry did fill the boots so well. But even there, Harry's performances are not so sacrosanct that someone else cannot put their particular stamp on the role.
I understand the Harry worship, but I can't agree with it. There were plenty of good choices for the role when they were first casting for Raiders and I bet there would be even more now.
As for suggesting someone for the role, I am not familiar enough with the current crop of actors. With Disney owning the rights now, who knows if anyone from Lucas, Spielberg to whomever would be involved in a next installment.