Backstory: I've been going to a few meetups regularly, particularly one that sponsors an expert in a field once a month. Recently shopify's co-founder Daniel Weinand was featured and the place was packed. There was little chance to ask questions or go deeper on a subject.
The Idea: A small paid meetup with an expert.
Deep Dive: You would build an events platform similar to meetup but the positioning would be towards premium, paid events.
Validation: You can sell tickets for meetup events but I've seen more people often link to event bright or a similar service. You can test this out first on meetup but as you gain some traction, a better positioned, premium (>$100) per event would be a good niche.
Monetization: You would take a percentage of ticket sales as a platform fee.