True, they did promise that 3 way hyper-car battle before the end of season 22 of Top Gear, after multiple delays thanks to McLaren and Ferrari arguing over what track to do the test on and what kind of tires would be allowed, and then before that could happen Jeremy punched the producer and didn't get his contract renewed as a result, so we never did get the test on Top Gear. So it's understandable they wanted to open with that test on The Grand Tour.

I do still think we'll see the Rimac vs Lambo vs NSX episode first this season though. It's just a good way to open a season, doing a battle between 3 expensive cars, and like you said, they will want to explain why Richard is on crutches, as well as why the Grand Tour tent isn't moving each week this season (Richard's knee injury from the Rimac crash and Jeremy's battle with pneumonia a few months ago are why the tent isn't moving this season, their doctor's ordered them to travel less until they've made a full recovery). 

Yeah, they set it up close to Jeremy's home in the Cotswolds this season, which is centrally located between James' house in London and Richard's house in Ross-on-Wye.