So you're making the assumption, that Chevy is going to disregard the J1772 charging standard and allow 277v just because someone previously managed to get a Tesla HPWC to work, even though the Tesla manual says not to....
Sure... that's sound logic.
When I got my HPWC back in May one of the installation options was to use two phases of a 480V three phase and I think the resulting voltage was 277V. I didn't look at it very closely because I was lucky to get 240V/48A single phase out of our box without major electrical work. I don't know where the manual went at the moment.
The HPWC supports a large number of installation options. Tesla uses them for destination chargers too and some of those have three phase available on the property. I expect that the HPWCs at many Tesla facilities are 277V.
I don't see GM as trying to compete with the 3; I see both companies competing for the 100's of million of new car buyers out there. Even the amount of people/companies/municipalities that want an electric car that won't be perceived as luxury is likely large.
For car shoppers comparing the Model 3 to the Bolt is like comparing a Toyota Yaris with a Ford Fusion. The size difference is about the same. There aren't many car shoppers out there agonizing over whether to get a Yaris or a Fusion.
The only reason people compare the Bolt and the Model 3 at all is that they are both electric. It's more of the EV ghetto thinking. The car industry has successfully ghettoized EVs into a niche of eco buyers and incentive seekers. The rest of the car buying public ignores them, even a lot of hybrid buyers aren't quite willing to go the extra step and abandon the ICE under the hood.
Tesla is the only company that has broken out of that ghetto. I admit to only being a mild eco buyer. I was not shopping for EVs. I started out looking at full ICE, but wanted a bit better mileage than what was available. Hybrids were mostly gutless as were the more economical ICE. I don't need super acceleration, but I want something decent enough to get on the freeway without being lunched.
I looked at the Model S on a lark and here I am. I would never seriously consider a Bolt, Leaf, i3, or any other EV out there. All but Tesla's offerings are compromised designs intended to only appeal to the eco/incentive buyer. They are all ugly things that scream to the world "I'm driving an ugly EV!", they are all small, and none are capable of a long distance road trip today. The Bolt may have a network in a couple of years, but 2018 would be 5 years after Tesla solved the problem.
The Model 3 should be compared to a Camry, Fusion, Impala, Accord, etc. That's what it really lines up against. It will be a bit more expensive, but it fills the niche of the mid-sized family sedan. I have a neighbor who wants a Model 3. He has a long commute of an hour each way and his gasoline bills are eating his wallet. He's currently driving an older Camry. For him the extra price of the car would be offset with lower fuel bills.
Right now most of the Model 3 reservation holders here are mostly people who have been following Tesla for a while and are enthusiasts for one reason or another. That population will probably make the Model 3 one of the biggest car successes in recent history. What might make it one of the very top car successes in history will be the mainstream ICE midi-szed sedan and other family vehicle buyers who switch to a Model 3. That will make the Model 3 a game changer on the scale of the Model T.
The Bolt may turn out to be the best non-Tesla EV to date, but it's kind of like being the best blues musician in the 1950s. Some people know of them and maybe they really are great musicians, but the mainstream music market doesn't even know that kind of music exists, or if they do, they never would listen to it. It took the revolution of the 60s when British musicians influenced by American blues became popular in the US that the mainstream noticed this genre of music in it's native country.