The router was by itself on a desk with rubber feet attached to give 8-inch clearance underneath with an 80 mm USB fan under it to increase air flow. Last temp reading was 114° C with only 7 users.
Asus Tech Support rep said we were the 10th customer this week with confirmed overheat issue with the 87U/R. They're working on new firmware and another new driver from Quantenna to try and reduce heat. No plans to change using thermal tape instead of the paste or use better quality heat sinks. Those are apparently $12 heatsinks. Router is in box awaiting RMA label.
114C is definitely abnormal. The vast majority of us have 80-90C top with ours (mine sits at 84C right now).
The current heatsink is sufficient, I bet just applying better thermal interface would greatly help.
I don't see how software could resolve the issue. Sounds like a generic level 1 answer to any unexplainable problems to me sadly.