No, that would probably irritate people, which is why people are gnashing their teeth at the thought of Whatsapp having ads. Having companies invade private conversations isn't just creepy, it's infuriating.

Your analogy doesn't fit to twitter though because this guy isn't having a private conversation; he's broadcasting his opinions publicly to the world. Imagine someone with a megaphone in an outdoor mall shouting about how shitty a company is. People would probably love the idea of a rival from another company engaging with that guy and saying "yeah, they suck, that's why I started this company, check us out." I doubt many people would find it creepy.

What if you were having that conversation so loudly that people inside and outside the Starbucks could hear you and when you mentioned a brand's name, they were immediately notified and your conversation was permanently associated with their brand? I mean you literally see this phenomenon in public where people converse too loudly in public and strangers then do end up overhearing and feeling, rightly or not, that they can jump in because a conversation that loud is simply too inviting.

Further: what about if I'd paid tens of thousands of dollars for a magic hearing aid that could pick out conversations in said Starbucks in which I have a potential business opportunity?

Twitter is public. There is the expectation (and intent) that anything you tweet can be replied to by someone else. In a coffee shop, there is no such expectation or intent.

Twitter is more akin to a soapbox than a pub.