I thought this was slightly funny.
Mark Zuckerberg is known these days for wearing t-shirts with Latin phrases on them, especially ones where he compares himself to Julius Caesar.
Bluesky made a shirt in the same style, but theirs says “a world without Caesars” in Latin.
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).
AP is flexible enough that you can do most AT stuff within AP.