I'm not sure how requesting a permit to install a new assembly line constitutes entering production this year. It merely shows they are moving forward on schedule towards production next year.
I don't think anyone said it means they were entering production this year, but I seriously doubt they're building the assembly line a year in advance. There's probably only around a 2% chance a production car comes off that line this year, but I'd say it's a much higher chance that it will be way before the projected Fall '20 production date.
Tesla (Musk) has a black eye for missing production dates. The S was late, which most people hadn't even heard of Tesla at that point. The X was a couple years late. And we all know the nightmare that was the Model 3 ramp up. I really think Tesla and Musk have given themselves a LOT of breathing room on this one - which may STILL mean Fall '20, which would be on time, and give Tesla some credit. But given 80% of the parts are in common with the 3, I can't see how they couldn't quickly ramp up the other 20%.
Another thing I've wondered about with the Y. There have been a LOT of talk of a new tax credit for EVs. If they believe that it is possible that the $7500 tax incentive could come back, they'll want to hold off and take advantage of the tax rebate. Let's face it, in reality, it is Tesla that gets the rebate. Just look at the Model 3, S, and X. Every time the rebate was cut, Tesla cut the price of the cars. Tesla knows what people will pay for their cars - and this with the rebate taken into consideration. So, if the market price of a Model 3 is $45k (for example) and the rebate is $5k, Tesla will sell that car for $50k. If there is no rebate, Tesla will sell it for $45k. So I'm sure Tesla realizes just how much they stand to profit and increase gross margins by waiting on the the tax rebate. Though, I'm sure they are moving full steam ahead with getting the car ready, but it would be a different type of urgency compared to the 3, where they were trying to get cars out BEFORE the tax rebate ended.