Add an "ignored" status
This would be a special category; any games marked as ignored will no longer show in the All Games section, and you would have to go to the ignored section to see them. For me, this would include games I got in a bundle that I have zero intention of playing, free games that I tried and didn't like (but still show up in my Steam list and would therefore sync to KTOMG), and software from Steam that shows up. I realize a lot of people wouldn't need this, but for those of us who like to micro-manage our things, it would be extremely useful.
Definitely planned, as well as the ability to “Hide from Others” such as games you may not want to display publicly when sharing lists.