SFO only has 2 exit lanes, and yesterday only one of them was open. My presumption is that both have the scanner (I didn't look for it on the closed booth), and it's located slightly before the booth window, so worst case if it fails you just roll forward to the window and talk to a human as per normal.

In busier times I could certainly see them having a dedicated lane. Hertz did this at some locations with CLEAR - some with a dedicated agent still there to assist on that lane, others where the agent from the next booth over had to come and help if you had a problem.