I've been crying for something like this for ages...

with windows phone 8.1 apps will suspended when user press the back button (so it wont be closed anymore , but developers have to implement this feature at moment calendar , some windows phone 8.1 apps are taking advantage of this )
 
with windows phone 8.1 apps will suspended when user press the back button (so it wont be closed anymore , but developers have to implement this feature at moment calendar , some windows phone 8.1 apps are taking advantage of this )

Lets say I press and hold the back button and slide an already opened app down(this closes opened apps on wp8.1) and immediately after doing that, i realize i still needed to use that app. I would still have to go to the start screen in re-open it.
What im suggesting is a quick gesture that would bring up the apps i used most recently so i can reopen the app there rather than going to the start screen again. (hopefully this explained it better)