The application to Google will likely be due early February. So the new
year is a good time to check the description of any projects you want to
mentor on the Octave wiki  and update the status as needed.
The GSoC 2018 mentoring organization application deadline is in about two
weeks, January, 23 .
Another good project for someone who wants to work on the GUI would
be to clean up the Variable Editor and then proceed to write a
Property Inspector. The graphic objects have so many properties
that it would be quite convenient to show them in a spreadsheet form
and be able to toggle the boolean properties, select from a list for
radio properties, etc. It's not my area of expertise so I couldn't
be a mentor, but I do think it would be a good addition.