Binder is honestly much better than D-Bus, but for various reasons I don't think we're going to see it much on desktop (though you can, in fact, use it there - and it originates from exactly such use).
The kdbus finally died when Linus sat down and proved that:
1) then-current userspace d-bus code was simply horrible
which led to kdbus being mainly about speed/latency, but...
2) Linus spent a weekend and got an userspace dbus server 80/20 solution that achieved better performance than kdbus
and
3) kdbus introduced no real new benefits that weren't ultimately triggered by "dbus is too slow", unlike Binder which involves fancy scheduling tricks to pass CPU quanta from one process to another along with RPC call.
Thus the final nail in coffin of kdbus (which was previously hampered by being considered too problematic to merge) was hammered in.
kdbus/bus1 were about making IPC primitives available race-free to userspace since the very first moment it is started. Perf was icing on the cake.
Binder is Google-only, so nobody else can really use it, given they might kill it at any moment.
The end result of not having bus1 is that we have to forget about brokered IPC and go back to 1:1 bespoke protocols over af_unix - ie, varlink
Binder has been mainlined since a bit before kdbus project started, and can be in fact utilized with alternate implementations, as the kernel interface is explicitly not married to any specific content of the IPC.
The kdbus finally died when Linus sat down and proved that:
1) then-current userspace d-bus code was simply horrible
which led to kdbus being mainly about speed/latency, but...
2) Linus spent a weekend and got an userspace dbus server 80/20 solution that achieved better performance than kdbus
and
3) kdbus introduced no real new benefits that weren't ultimately triggered by "dbus is too slow", unlike Binder which involves fancy scheduling tricks to pass CPU quanta from one process to another along with RPC call.
Thus the final nail in coffin of kdbus (which was previously hampered by being considered too problematic to merge) was hammered in.