A critical issue with a course or part of a course in a parking lot is specifying the precise limits of the route. It gets more complicated, as everyone who's ever done it knows. I think making a distinction between a road and a parking lot is kind of silly, but aside from that rules clarification issue, we probably need to take extra care in specifying (even to the point of redundancy) exactly where the route lies. Beyond that there are the questions of how permanent are the reference points we are using, will the RD interpret the specs as we intend, etc. Of course the same kinds of issues come up when all or part of a course is in a park.
Retrack vs. road: Time was, there was no such thing as road records. I wonder if we are now at a point where a road record is "stronger" than a track record? I reckon a runner on a track could save as much as 30 cm per lap or 1.2 m per "mile", as opposed to any amount of SCPF run in a road race. On the other hand, it has now been established that humans cannot run as well on a turn as when running straight. Just wondering.