While I agree with where you’re coming from: Dart isn’t going to last past probably Pittsburgh and guys like Matt Miller are saying it’s very unlikely he’ll last past the first 32 picks:
Miller:
ESPNs Justin Reid says Dart is QB2 on some boards:
Link to above quotes
There’s over a dozen aggregated mocks that have PIT picking Dart at 21 on Mockdraftdatabase from writers.
In short I don’t think the saints will be in position to even trade back up for dart. Best case scenario is if they trade back with like the bengals or something and take Dart at 17(Seattle at 18 also has interest)