A group of us have done this dive 2 years in a row, and were planning on trip #3 for this year. In one of the articles I read about this, a Ranger acknowledged that only about 10 divers a year hit the lake. The risk of invasives is pretty minimal; realistically, a much greater hazard to water quality comes from the gasoline engines on the tour boats. Fishing is also allowed, and not at all policed- no license required, and no check for live bait. I believe there's still a competitive swim where people are dropped off at Wizard Island, and then swim back to the trail. All those folks are in wetsuits, and there are more than 10 contestants. Haven't heard anything about that being stopped, but since the previous swim in those wetsuits was more likely to be fresh water than salt, that's another exposure (all of us had completely dry drysuits, and our previous dive had been in salt water). Not to get political, but my experience with a lot of government employees tells me that although they may mean well, deep down it's about control. "How dare people enjoy this lake without us being able to stop them", that sort of thing. They're human, with human biases, preconceptions, etc.
As far as dive safety, I definitely recommend nitrox, along with a hefty acclimation period before the dive. Take a good long rest after the dive, hydrate well, and take your time hiking out. It's 1.1 miles down, but it totally feels like 11 miles back up. You should definitely be in good physical condition for this dive, and it helps if you can share weights (and even other gear) among the team.
