Thankfully GEO is still a bit self cleaning as Sun and Moon influence makes it unstable - you can clearly see it in orbital debris models, there is a blurry plane shifted ring around the primary GEO stripe.

Still that will only prevent a dead sat in sitting in a valuable spot for ever, it migh still drift the wrong way and require active sats to do avoidance maneuvers, not to mention the chance of two inactive sats colliding.

Self-disposing satellites are a good idea, but it's not perfect. If the control unit or the engines of the satelite fail too early during the satellite's life span, the thing will simply stick around.

Right. And this actually is rocket surgery.

There's also the problem of retaining propellants over long periods without experiencing some negative consequence (detonation, unintended firing, volatilisation, etc).

But in general, minimising the special-handling cases would be an improvement.

Long-term propellant issue could probably be solved by using a cold-gas thruster with a non-reactive propellant - basically a pressurized gas tank welded to a valve and a nozzle. It should have enough Δv to push you into a graveyard orbit, or even deorbit straight from GEO (though that's probably dangerous, and I imagine you could see spectacular fireworks from the ground, as the satellite would be hitting the atmosphere with a couple km/s more velocity than it's typical).

Solid thrusters being another possibility.