Despite understandable misgivings with ATProto due to its corporate origins and its architecture lending itself to centralization, it's still open source. Moreover, it serves a different purpose compared to ActivityPub, in that it specifically aims to enable and support larger scale social networks.
In a way, ATProto could be complementary to ActivityPub, but for this to be the case, there needs to be more shared understanding between both communities. People working on both recognize the faults in existing social media, and aim to address them in different ways.
ATProto provides an opportunity to break down big social media enclosures with data portability and a similar vibe to big social media, but with more individual empowerment to adjust what they see. The latter point is a commonality with ActivityPub, but ActivityPub provides a different angle of breaking the big social media enclosures.
Where ATProto serves the interests of those into big social media vibes, ActivityPub serves the interests of those into small social media vibes. In other words, ATProto scales up, where ActivityPub scales down.
ActivityPub is arguably a better protocol for both individual and "small" group empowerment, as it can enable otherwise less active, small platforms to connect and ensure there's always some level of activity to encourage people to come back. Think of old forums that, on their own, gradually faded out as people stopped visiting and posting for more active online communities. ActivityPub can serve as a buffer against that, to some degree.
Together, both protocols could provide a better, open social web, and perhaps effectively topple big social media enclosures. After all, who wouldn't like to see the web without Meta/Facebook and Twitter/X?
TL;DR: ATProto/ActivityPub have a common foe in big social media enclosures like Meta/Facebook and Twitter/X and would be better served working together to erode their influence.
True, but as noted, it isn't a necessity to run a full-network relay, which those resource demands and costs relate to.
At the same time, one of the larger Mastodon instances, Mstdn.social in terms of financial costs alone amounted to about 1000 euros per month as of October 2024.
The architecture of ATProto also enables a greater degree of flexibility in separating out costs by comparison, which in some respects may be an interesting model worth consideration for new or developing ActivityPub software, and in some respects is already in the works with projects like Bonfire and ActivityPods. On the ATProto side there's already at least one person looking to adapt ActivityPub to ATProto's PDSs in a manner similar to ActivityPods, just using ATProto data formatting instead.
As most of the people here, I'll really believe ATProto is federated when there's a non Bluesky owned instance to register on