I realize that it's been awhile since my dogs have been in trials that run in 2 rings at the same time, but there are ALWAYS distractions at trials. Dogs barking, other courses being built, dogs warming up, dogs playing in the background. At my last trial, there was a youth 5K going on in the same park in view of the dogs. No one was bothered by it. (and it was funny, because one of my friend's dogs ran into my dog's ring and bopped into him. Kaiden hesitated and looked at the dog like "hum... that was strange!" The judge told us we could rerun it, but we were clean already, and I chose to finish. We finished the course fine for a Q. Never had that happen before, and in one of the classes we struggle with, but my dog recovered within a second.) We even in the past had army helicopters flying over our trials in IA and only a tiny handful of dogs had trouble. Distractions should be well tolerated by the dogs entered at Champs already. JMO. I personally would like to see 2 rings running concurently at Champs to speed things along. Dogs might be a bit distracted at first, but should be able to adjust. That's what is great with Pre-trial runs. Your dog gets used to being in the big arena before the main "show". It's not uncommon for dogs to be a bit more nervous there. Heck, as a handler, I sure am. And, twice now, my Veteran (soon to be DD dog) had a major panic moment at Champs. But, I was able to refocus him and we Qd on our runs. Maybe put the DW at the far end of the ring. But, distractions are nothing new for agility dogs. Certainly not as fast as our courses run and how much is going on around them all the time.
On one more note, 2 rings were running at the same time with Pre-trial last year, and although I wasn't watching many runs, it didn't seem to be a big issue. Dogs handled it fine.