The use of smart folders would be very helpful. Papers3 had this feature, and it was very frequently used to tag new articles so that they would appear in the smart folder, without having to do any extra steps, such as drag/drop/load/scroll etc
Smart Lists have been implemented and instructions to create them can be found here: http://support.readcube.com/support/solutions/articles/30000037316-smart-lists
I'll add my voice to the choir...
Yes YES. it's must!!
I third this request (and add that it needs to go into the iOS app too!), please!
please do this
I'd second this request. Used this a huge amount with Papers3 to help keep my library curated