I'm reluctant to embrace an adventure race style to an orienteering relay. Maybe the relay format can't work - i.e. people don't find it interesting enough, but I want to organize a relay, not an AR.
And @coach, the US relay championships is often de facto its own event. Consider the 2017 Relay Champs
in Los Angeles this March - there were a total of 11 3-person teams in all categories. Perhaps the event struggled because of its format of Pre-O, Trail-O, Relay, and Middle, but that attendance reflects complete disinterest in the relay format.
For my own part, grad school precluded too much cross-country travel, but it would have been hard to motivate a 6-8 hour flight to run 9.5 km of orienteering. The amount of quality orienteering I get to do is a major motivator in determining these travel objectives.
Realistically, I think 4-8 km of orienteering the day before a Highlander shouldn't have much impact on performance the next day. I guess the only way to find out is to try both approaches and measure the results.