Backstory: A few months back I was sitting around the dinner table with some friends and we got to chatting about trips we wanted to take. Julia started the conversation with "I've always wanted to visit Niagara Falls." My other friends chimed in that they've never been and it was on their bucket list.
I was surprised that everyone had this trip on their bucket list and they have never been (we live in Baltimore, a 6hr drive). I've already been but now I'm going for a third time in two weeks :)
The Idea: Fill out your bucket list, link with friends and see where you overlap.
Deep Dive: You would have to get enough people on the platform in the first few weeks for this to take off. Most likely you would piggy back off facebook or instagram to help link friends accounts. Initially you could force facebook login and parse their likes to suggest bucket list items.
Validation: This notion worked for us in a conversation around the dinner table.
Monetization: You would have to run ads on this platform. I doubt anyone would pay for this service.