"But Musk is said to want to start construction extremely soon and aims to have Model Y vehicles coming out of the plant by the end of the year." That is just delusional.
I think the rule with Elon Musk is all his estimates are extremely optimistic and you need to multiply them by two or three to get closer to reality. But I'm sure it serves a purpose in giving his employees an aggressive target to aim at. Even if they miss it, at least they probably got there sooner.
That would require an executive board entirely detached from both reality and what their own experts have to say regarding the feasibility of those plans.