I built exactly what you describe at Flights With Friends. But the thing I learned is that group trips are not a democracy. Trips without a dictator who makes the decisions don't actually happen.
Building tools for the dictator is hard because getting the other group members who are not the dictator to actually use any tool is too much work. You are always dependent on the least reliable member of the group.
This is the exact reason that travel cost splitting tools don't work and the dictator just ends up paying for everything and getting the group members to pay them back. If they used a bill splitting tool the flights and hotels would sell out before the slowest member of the group put in their credit card.
As the self-declared benevolent dictator for several trips I've planned, I agree with a lot of what you said.
I've led a couple of great group trips to places I'm passionate about by emailing a group of friends and essentially saying "I'm going to go to X, here's what I think is amazing about X, and here are the proposed dates", and essentially getting folks to opt-in or not. Once the trip is locked in, there's certainly some discussion and folks say "I heard there's Y in X, let's do that!" and there's probably time to for that activity. But yeah, you need one master of the itinerary.
I do disagree somewhat about the cost splitting thing though - I've had several good experiences using SplitWise, although the groups have been relatively small - from 3 to 6 people or so. Maybe if you have more people, or weird family dynamics, or technophobes, it doesn't work out.
You are absolutely correct – Splitwise is great. I was thinking about the failed startups that did the splitting before the trip and then pay the vendors directly. Splitwise makes the process of getting reimbursed much better.
Also benevolent is the right prefix for dictator in this case. This person's reputation is on the line and they are working hard to make sure their friends/family have a great vacation.
Building tools for the dictator is hard because getting the other group members who are not the dictator to actually use any tool is too much work. You are always dependent on the least reliable member of the group.
This is the exact reason that travel cost splitting tools don't work and the dictator just ends up paying for everything and getting the group members to pay them back. If they used a bill splitting tool the flights and hotels would sell out before the slowest member of the group put in their credit card.