This is all technically possible, but then there's also the privacy/security aspect. Many who would actually be into a solution like this won't be too hot to share the necessary information in the first place. And with good reason: companies with the resources to provide a decent experience don't have the best track record of protecting user data, and ensuring only the user has control of it. The privacy conscious would rather self-host, and end up losing out on capabilities in the process. So it's a sort of catch-22.
Part of the big challenge here in my mind is that companies are reluctant to put data into the world for others to consume in a friendly way - if, say, event organisers, put data out as open-API's, there would be the opportunity for a self-hosted or "convenient" third party (ala Google, Amazon) to create conversational experiences on top of it - private user and privacy uninterested user is well served (as is "event seller" as it's exposed to more people). But, as long as we're stuck with systems having to pull data by web scraping, no one can build a good solution that could work for either scenario.
I'm the case of events, I'm not so sure. Ticketing platforms want to drive sales via easy discovery and wide distribution. Take Eventbrite as an example (disclaimer: I used to work there). They
