I don't know about Scrivener, but thought about pros and cons for a different topic in search of a new home. Concentrating on the difference between Cake and either of the other two options:
- Cake allows anyone to write about any topic. This is technically true for the other two platforms as well, but both are organized in a way that allows some users (moderators of the subreddit / community with the biggest reach) to influence the conversation more than others.
- As a special case, Cake doesn't have any form of "downvoting", which is a Reddit feature that is really irritating to me.
- Cake allows everyone to be the moderator in their own conversation about some topic, especially when a conversation is started as a "panel". For example, if there's a small group of people that you want to be heard by everyone (Scrivener developers invited to a Q&A by you?), you could start a panel where they, but not anyone else, can write.
- Cake allows conversations to be categorized as belonging to more than one topic. On Reddit, you can post to one subreddit or another; on MeWe, you can post to one community or another. You can not post to three different subreddits/communities at the same time. As an example, perhaps you want to talk about how you are using [Scrivener] to write a [Science Fiction] novel, and ask for [worldbuilding] advice in that context. On Cake, you could add your conversation to all three topics at the same time, which in theory might get you a bigger audience of people that are interesting in one but not necessary the other topic.