In my games I've found 2 Motherships but don't have the fleet to deal with them yet (3 frigate + dram scouting force). I've also found a bunch of "clues" that I haven't gotten to yet because they are on the other side of the sector. The current filters of week/month/cycle work well for things with a time limit like bounties, but aren't very good for objectives that the player would like to remember but won't be dealing with anytime soon.
Suggestion: Add another filter next to week/month/cycle: saved. Then add a checkbox somewhere on the log entry itself that saves/unsaves it. So if I find a mothership, I can open its log entry and save it for later.