Better traffic: Apple's already admitted that it's been collecting anonymized information from iOS device users to create "a crowd-sourced traffic database." While traffic support has been built into mapping on both Android and iOS for a while, it could always stand to have its reliability improved--current predictions can often be hit or miss. By taking advantage of the millions of iOS devices in use, Apple can potentially use that data to build an even better model of traffic situations in real time.
Offline mapping: Another Android advantage: Its turn-by-turn implementation caches data about your route so that if you lose network connectivity during your trip, you won't lose all your data. That's a good way to strike a balance between the convenience of downloaded maps and their hefty sizes; it's definitely a feature Apple should embrace.
Cycling directions: On the Web and on Android, Google Maps offers the ability to provide directions for cyclists. That's not only a handy feature, but it's an important one: Biking directions often conform to neither driving nor walking directions. Not only could it help cyclists create more efficient routes, but it could have a positive impact on safety as well, helping ensure that cyclists don't find themselves in a dangerous traffic situation.
Preferred routes: Making directions smarter always gets a thumbs up. Speaking as someone born and raised in a city where you're more often than not told "You can't get there from here," it'd be nice if the mapping data could be improved to take advantage of local knowledge. Whether that can be accomplished by harnessing traffic data to figure out how to avoid congestion spots, or otherwise analyzing routes that travelers commonly take, is unclear. It's a challenging problem to solve, but the rewards of having best-in-class directions extend beyond just bragging rights.
Multiple stops: Ever need to figure out the most efficient way to make pick up a friend on the way to your destination? On iOS, Maps are a strictly location-to-destination affair. But Google Maps on the Web allows you to add subsequent destinations, helping you plot complicated routes to multiple places, potentially eliminating redundant or convoluted parts of your route.