I would definitely buy a Roomba for my lawn (assuming it worked well). Obviously more safety concerns than a vacuum cleaner, with the spinning metal blades and all, but seems doable.
Existing lawn robots still mostly rely on a buried cable to form a boundary-line. The next generation vision/lidar/gps systems are clearly in development but not commercially available in the US (the Segway NaviMow is available in Europe).
This year was the tipping point for the US market, they weren't readily available until late summer. I'll have a (ground) wireless lawn robot next year one way or another, it would bring me more satisfaction to build one but that doesn't mean I'll actually do it.
That's new — but those are still $5000 models "designed for professional fleet use", a little on the steep side. I'd give it a little longer for that to percolate downmarket towards the likes of the Navimow which is around the €1500 level.