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S&P membership is ... possibly even a fund mandate requirement for many active investors to be able to purchase Tesla.
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I agree with most of your post but for the quoted part above. This might conflate another very important issue that the conditions leading to S&P inclusion could also affect. That is that many institutional debt buyers (principally pension funds, insurance companies and various governmental investors) are required to meet some specific interpretations of what is called a "prudent man 'sic' rule". ['sic' because this will become 'person' sometime.] Those interpretations and/or rules usually require some period of profitable operation and also an investment-grade rating. Tesla could well achieve an investment grade rating if continuous profitability and positive cash flow coincide for some time with obvious positive outlook. If THAT happens we will see major share price escalation and more boradly based institutional holdings.
Almost all the discussion here and elsewhere is about S&P. That is indeed important. However, the catalyst for broad secular short-defying institutional holdings will be positive cash flow and positive earnings.
Ancillary but crucial points will be proof that Tesla can thrive without direct government intervention and proof that Tesla Energy has substantial broad customer appeal for residential, commercial and utility customers. These ancillary points are necessary in my opinion because the auto industry has repeatedly burned institutional investors. Huge though it is, worldwide auto industries have repeatedly been bailed out by governments trying to protect jobs, which increases risk to institutional investors.
Just consider these when thinking of how much negative institutional sentiment is driven when considering direct government intervention staving off rational business decisions for; (GM, Ford, Renault,FCA, DB, VAG etc). Then consider the effective control of; (Nissan, Toyota, Mitsubishi, Hyundai). I exclude the Chinese because their positions are generally explicit and their business models are built almost entirely on official Chinese government support.
When considering the auto industry and the public utility industry globally we see Tesla truly disrupting both. Apologies to the Christensen Disruption theorists but they really do not understand that their own auto industry analogy proves Tesla. The Models 3, Y and Cybertruck are mass market by their definitions, even though they aren't the absolute bottom of their markets in initial price but they ARE on Total Cost of Ownership. Still, Tesla Energy is absolutely the cheapest and best option for "peaker" power plants which are a much bigger market than are cars.
As that last paragraph becomes more broadly known and Tesla has consistent positive cash flow and GAAP profitability S&P inclusion will be good but dwarfed by comparison with the virtuous cycle commencing with investment grade.
Anybody wanting a long LEAP should forecast when investment grade will happen!
What will happen then? Tesla debt will suddenly become appealing to gigantic pools of funds so cost of funds will decline by probably >100 bp and inventory carrying cost will decline similarly. Thus, GAAP will rocket upwards.