As for Aladdin, it'll be impossible to find someone who will surpass Robin Williams as the Genie but you never know, the actor they choose may still add a new and unique side to the character which could be interesting. I don't really mind about the race of the actors, it would be nice to include some people genuinely from Arabia but acting talent should be the main focus.
The visuals is one thing the Disney remakes all get right - the CGI and scenery is breathtaking to say the least.
I love David Bowie and think he would have been perfect in a Disney role - he was amazing in Labyrinth. I think the Moana villain, Tomatoa, was inspired in part by Bowie but it's not the same thing.