Never in the history has a domain ever sold for anywhere near that amount.
Cars.com as business (valued at $2.5 billion) was sold where the valuation of the
domain itself was reported as $872 million. If we ever get to see bitcoin dot com get sold, it will be done through a similar construction, because if you sell just the domain without a working business it's worth waaaay less.
I don't think any entity within crypto has the capital needed to acquire this domain including the businesses, unless they throw in shares of their own company to tempt Roger to sell it. If we get to witness a takeover, it will probably be an institution or large social media platform. I rather see Roger keep it in his portfolio than for example Facebook or Google.
No single entity would able to buy it for sure but im not saying that there were no billionaires out there.Asking for Billion does really need some justification but as you said if its just a domain then its way too less as expected.Giving out shares is really a tempting one but with Ver current standing i dont see that he would care for such offer but were pretty sure that there were already big institutions that eyeing out this domain.Its might not be that expensive or worth billions but this one can give a fortune if its being utilized well.