Again, if you look at the original contract, Schedule 3 names Miles Morales BY NAME, Schedule IV states that Spider-Man/Miles Morales can be used as an alternate named Spider-Man costume, and Schedule VI names Spider-Man III (Miles Morales) as a 'Named Character' that SPE is authorized to use in their production. I don't know how much more cut-and-dry that can be.
Now, whether that's a good idea, whether it happens or not, or whether it should, all that is irrelevant. I actually don't think it'll happen, and I don't think it'll be successful if it does. However, the contract is what matters, and it's there in black-and-white that by the terms of the original agreement, SPE is contractually allowed to.
As for Stan Lee's interview, while I always like hearing his thoughts about Marvel's processes, is an opinion piece at best, and as one of the co-creators it's obvious that he'd want the character to remain as true to his original vision as possible.