As far as Miles Morales goes, there is one significant hurdle that can't be ignored, to the majority of people who might potentially see a Spider-man movie, Spider-man is Peter Parker, it is not about racism, it is not about being a angry troll or a fanboy who can't let go of the past, Spider-man has been around long enough to have a place alongside Clark Kent and Bruce Wayne as pop culture icons.
Additionally, we have already seen a prior trilogy that was heavily based on Marvel's prime universe and that trilogy has it's own set of fans that have based their vision of the character on what Tobey Maguire did as the character.
To put it simply, Peter Parker is Spider-man as far as just about everyone is concerned, not much is going to change that, it would be like saying "Hey, lets mix things up and have Jean Paul Valley as Batman in the next movie!" Nobody would know who Valley is.
Morales is a great idea in the comics but it worked out in the comic because of two major reasons.
1.) It is not part of the primary Marvel universe, Peter Parker is still Spider-man as far as most casual fans go.
2.) The story that brought us to Morales was handled really well and his character taking up the mantle made sense, it had the benefit of time to really work.
To be a bit frank, I can't help but feel that Bob mentioned Morales not because of his quality as a character but simply because he is not white and that somehow not being white makes him a more interesting character by default, I can't say I share in that idea, I would love to see The Amazing Spider-man franchise tackle Morales but only if they are willing to put the legwork into allowing that story to happen correctly, not just to please those that seem to think that male and/or white characters are boring or don't do a good enough job at scratching that social justice itch.