I find Baidu Maps to be pretty useful wrt identifying optimal exits, but it would be sweet if there was an app (or website) that focused exclusively on subway station logistics.

For example, I now regularly travel between Xujiahui and JA Temple. This is a pretty simple Line 9 to Line 7 drill, and I figured out the proper exits in short order. However, I managed to reduce my average door-to-door time from 30 minutes to 22 minutes via trial and error optimization, including a big tip from a colleague about an elevator near JA Temple Exit 6 that goes directly from the ticket gate level to street level. Few people, even regular commuters, know about this elevator because it is at the end of a hallway behind an ATM machine.

Other optimization examples in the instant case:
-when transferring from Line 9 to Line 7, door #12 gives you the fastest access to the stairway so you can almost certainly get there before the gridlock ensues
-on the way back, anywhere in the middle of the train is fine, but instead of using the stairway, take the escalator up to the ticket gate level, and the elevator back down to Line 9 level; it is within spitting distance of the top of the escalator
-assuming Xujiahui is the destination, you want to be in the middle of the train (can't recall the optimal door number off hand) so you can take the elevator up to the ticket gate level
-morning rush hour honestly isn't that bad --in fact, I manage to snag a seat on Line 7 occasionally-- but, when I find myself near JA Temple in the evenings, I usually plan on hitting the gym and/or eating there because leaving at 6p or 630p is completely nuts
-slightly off topic, I often use Didi on the way back, but wait times have been 30+ minutes since the weather turned cold

Back on topic, if someone were to go to the trouble to collect user generated feedback (i.e. no need to send your own staff out on missions when millions of people are at your disposal) on logistics like these and present it in a clear manner, I would get onboard even if doing so entailed enduring receiving obnoxious push messages. I'm guessing that whoever launched Exploreshanghai had this in mind pre-launch, but they never made it past the "same subway network map you can find on Google" phase.

ETA: When in doubt (in Shanghai), position yourself near even numbered doors because odd numbered doors are often (usually? always?) at the car ends. In addition to increasing your odds of scoring a seat, being in car middles ensures that you won't get stuck in the "nothing to hold onto" zone between cars.