I'm going to go ahead and finish this up.

Current status:

I think we'd just redirect people to the correct route -- this would allow instance admins to set it to anything they want without modifying the app itself. For example, they could even choose a default blog to land on if they're running a multi-user instance.

So let's say I set default landing page to about. Does it means that when visitor lands, he/she will be redirected to /about, or will stay on / but about page will be rendered there?

Just to add: https://distbin.com adds the original URL to the cc property on the Create activity.

From certmagic:

Remaining work here is mentioned in T536: Compile all static / default assets into binary.

Nice! Good to know.