@Mix Android there are a few things wrong with about messages. One of them being that they don't indicate what they reference, so you have to have the referenced message in order to know what kind of about it is. Secondly lets say crut becomes a hugely popular way to build applications, then you are going to have a ton of about like messages. They could be from a number of different type of applications. Depending on the application, you might even have more of these "change" messages that normal messages. In any case it would be better to use specific app/update type of messages and put those in the subfeed related to app, than to put a lot of unrelated messages into the same feed.
Right, a very good subfeed candidate would be "profile" abouts. That would mean you could really quickly onboard someone as 500 feeds * ~5 about messages can be done in roughly 1-2 seconds. After that you could start getting what other data you might be interested in.