4) don't overestimate cut of transaction and underestimate ad revenue (promoting the transaction seekers). Let's use Amazon as an example: They run a 3P marketplace with a transaction cut business model, and it's not very profitable. Vs. their ads based sponsored product which is extremely profitable (soon to larger than AWS for profit at Amazon). This is a very different ad business than twitter's current performance marketing ad product.
I think first party ads promoting commerce on your platform can be very lucrative. And % of transactions tend not to be, with the exception of Android / iOS app store markets.
I haven't done the math because nobody is paying me to. But your example of Amazon might reinforce my point in that all three components (retail, ads, AWS) reinforce each other. Amazon is trying to be the "Everything App" also because they see synergies (even if only in shared infra).
And Amazon can afford to be less agressive with ads because it's a smaller part of their business, compared to (e.g.) Meta or Twitter. Apple is in a similar place: they can afford to care more about privacy because they don't make money from ads.
The more revenue Twitter can get from non-ad sources, the better the user experience (in my opinion).
But you're right that there's no guarantee that they will be able to get much non-ad revenue.
I think first party ads promoting commerce on your platform can be very lucrative. And % of transactions tend not to be, with the exception of Android / iOS app store markets.