I love the webhooks feature! I have some critique to offer, though.
First, it seems like the permalink/URL would be central to the post/topic events, but this is not included in the payload. It's not a big deal since I was able to build the URL myself from the properties provided, but it seems logical that this should be added for topics and posts in the post stream.
Second, it looks like only the cooked posts are delivered. Receiving the raw posts could be useful, too, if that's possible, especially when used in an application that doesn't parse HTML.
While I appreciate the copious number of properties sent from topic and post webhooks, some of the data seems irrelevant, like
unseen, among others. Not an issue at all, but some fields may be unnecessary.