

ActivityPub already existed when they started BlueSky. They chose to not make their protocol compatible.
Traditionally, that’s what new major version numbers are for. IF (and I stress the “if” because I have no clue about protocol design) it turns out that AT has useful features, a merger of ideas of both ActivityPub and AT could lead to ActivityPub 2.0.
That would be somewhat similar to AMD’s proprietary Mantle leading to Vulkan (which was originally intended to launch as OpenGL 5.0).
At least in Germany there is a mandatory German filter list that seems to be maintained by Bluesky themselves. They couldn’t legally operate here if they allowed holocaust denial and such.