They have been focusing on improving X-Apps, their collection of GTK-written programs for their distribution. They have made a number of improvements to the Xed text editor, including search support for regular expressions, switching between tabs with the mouse wheel, support for Python extensions, and much more.
Linux Mint has also been working on their Xplayer media player with refinements to their user interface, keyboard control improvements, subtitle files are now automatically loaded, and fixes to the on-screen display.
In other Linux Mint news, they are working on Bluetooth improvements for the upcoming Linux Mint 18.2 release.
More details on the latest Linux Mint developments via their blog.