Ravnica can only work if you do a specific story set in Ravinca or if you just use it as a backdrop. I believe the original Ravnica trilogy was something of a police procedural, which works excellently in a busy city, while Agents of Artifice just used it as a backdrop. Either you explore all of Ravnica or you do nothing with it. I don't think there's a useful middle ground there.
I think there is a difference when you're speaking of the presentation between a novel and a movie. In a novel, essentially nothing that happens out-of-focus happens, essentially. In a visual media such as a movie, you can saturate the presentation with a lot of little world-building visuals such as what we see from the card arts to form a more realized-feeling world (note: I'm not saying that they will actually do this properly, just that it's possible).
Hm... Actually, this makes me wonder how they'll go about presenting a movie. Which is more expensive: a live-action movie with exotic make-up and CG special effects, or a fully-CG movie? My gut says a full-CG movie would be cheaper, considering the number of sets and makeups they would potentially need to create for an M:tG movie. Any M:tG movie marketed to the masses (as opposed to block novels which are specifically made to paint the associated plane) has to include multiple planes, with theoretically vastly different races between them, and most races don't even look the same from plane to plane; that's a lot of sets and makeups to design for unless you only show like 10 people on each plane.