Add the ability for Filr to index EXIF information in pictures (RAW/Jpeg/etc), including picture info, dates, GPS data, camera info etc. This would bring it inline with features in many online services. Ideally it would do it without loading all the images into the filr server (ie. just read the EXIF data of images on net folders for example.)
Just further to this, it would appear that this should not be very difficult to implement considering that Filr already appears to be using Apache Tika with Lucene to some degree, and Tika can easily be configured to read the EXIF using Class ImageMetadataExtractor.