@phiofx Just this morning I was thinking about this! Not activity pub, but how the "github homepage feed" is increasingly becoming people's (well, programmer's) window to the world. However, their feed algorithm is pretty basic currently (e.g. comment likes etc are not surfaced anywhere) and I was musing to myself what-ifs about how to make it more like, say a twitter/reddit alternative.
And activity pub would be a solution to this indeed! Hopefully gitlab's support triggers GitHub into following suit too. Building decentralized-yet-centralized feeds then would become possible. In my experience so far, GitHub has always seemed to care for the end-user (programmer) still, so they might follow suit, fingers crossed.