I agree. I definitely think we're due for a proper coaster (and boy, I'd love one!), but unless they can make one that's almost completely silent, I don't think it'll be happening anytime soon. The park already receives complaints from Halloween Horror Nights, so I don't think a year-round coaster would ever make it past the snuff test at the park. I'm not sure what Disney did, but I don't think it'd work for a full-fledged coaster like you proposed.
If they do manage to solve the noise issue (and this is a big if), I'd love to see something on the scale of Hollywood Dream in Japan here in Hollywood. It doesn't need to be thrilling, but I think it'd be a great opportunity to offer sweeping views of the San Fernando valley.
Speaking of views, what about a PeopleMover?