Maintenance of the software, and some practical issues for fully autonomous vehicles.
We're probably all aware of corporates still running Windows XP. Not recommended but it happens.
I recall when ABS and all wheel steering (on consumer cars, it was a fad for a while) were "new" Tiff Needell* expressing on TV concerns about the likelihood (or not) of maintenance being properly arranged by the third or fourth owner of a vehicle.
Software is improved all the time (until manufacturers "bin" it, as they have done with my otherwise perfectly fine PBX) but considering the number of times when I update a copy of firefox and learn that the various plug-ins I have previously installed are not compatible and need to be removed, reinstalled or tweaked, do we really have confidence that these self driving systems will work and be maintained as intended? Given the lack of adherence to current mechanical standards by drivers, which are easier for traffic police to spot (where they have time) than electronic issues, probably not. I know my local Volvo main dealer has to connect a car to the head office servers for any updates, he doesn't hold a copy himself. That's great for ensuring that cars where the owners can pay the high costs are up to date, but not for those using independent garages.
Also for those of you hoping for a totally autonomous driving world: I get to my field in my Landrover (or similar) and need to drive to the other side of it to pick up the carcass of the sheep that needs to be removed and taken to an authorised disposal point. It's unlikely to be waiting for me on some convenient track. Do I need to swap vehicles, perhaps having to leave a "manual off roader" in each contiguous area that I farm? No. Its not practical or economic or particularly environmentally friendly (from an equipment efficiency/lifecycle point of view) for a small farmer. Manual/Dual control vehicles would remain a necessity. Likewise for the ambulance driver/fireman/vehicle recovery operator who may need to carefully negotiate past a queue of traffic by using a non-authorised driving surface on a temporary basis.
All this stuff is a lovely idea and I'd be pleased to see it happen with all the benefits it might bring, but I think its probably going to be a lot more complex and expensive than many of the proponents would have us believe. Still, their interest is sales/profit and hoping that the costs of the problems (infrastructure, inconvenience) will fall on someone else. Thats only human. Ironic in the circumstances....
*for the younger reader, he presented Top Gear before our lord JC** ascended to head up the current trinity.
** "He's not the Messiah"