How? I mean, what non-crypto not illegal thing you actually can currently purchase without going via fiat?
Prices are pegged to fiat but the merchants accept BTC directly.
Further, what percentage of those companies will continue to "accept" bitcoin if they are no more allowed to convert them to dollars?
Remember that every actual Bitcoin transaction requires, on average, paying a $17 transaction fee to pay all the miners and the electricity they used in processing the transaction, so you don't want to actually be sending it between people often.
I don't think Tesla would keep the revenue as Bitcoins because the accounting implications are pretty weird. This is from Tesla's 10-K, via FT [1]:
"We will account for digital assets as indefinite-lived intangible assets in accordance with ASC 350, Intangibles — Goodwill and Other. The digital assets are initially recorded at cost and are subsequently remeasured on the consolidated balance sheet at cost, net of any impairment losses incurred since acquisition."
You sell a car for Bitcoin but then you'd have to record the revenue as intangible goodwill on the balance sheet? That would mess up their results.
It's worth noting that Tesla includes US government bonds as cash equivalents, but isn't able to do the same with Bitcoin.
[1] https://www.ft.com/content/364734d1-80df-49d3-bc2f-c813c9306...