> You're talking about memfd, I think? That has nothing to do with kdbus in particular. It's an independent syscall that replaces many use cases for splice/vmsplice, even though it was introduced as part of the kdbus project - it's still a separate thing.
That was created for KDBUS but has more use than than being used for KDBUS exclusively. It still was written for KDBUS.
And so it was accepted and merged. That something good came out of kdbus is excellent, but that's no justification to merge in the whole package. A ton of proposed kernel additions end up like this - a few good ideas refined and accepted, and the rest thrown out.
That was created for KDBUS but has more use than than being used for KDBUS exclusively. It still was written for KDBUS.