That’s what basically happened in Germany like 10, 15 years ago when the first publisher had that idea. Its news stories would still show up in search results but only the headline, not that text snippet and no thumbnail image. These results were less attractive to users, so traffic from Google to those web sites crashed down by like 80, 90 percent.
In the end the publishers gave Google a free license to reproduce text snippets and thumbnails. The tightened copyright law provision wasn’t repealed. Small search engines without leverage still (AFAIK to this day) have to pay.
So Google pays nothing, publishers earn nothing, upstart search engines can’t afford the fees, and so Google leaves even more in power because of a law not even they wanted.
Coca-Cola could have an official profile on mastodon.social and use hashtags there as well. Whether corporations use hashtags or not in their “regular” Mastodon posts has nothing to do with Threads.
Also Mastodon has user-level features to restrict unwanted content to show up in your feed ranging from hiding boosts up to blocking the entire instance:
And since Lemmy cannot interact with Threads content at all, defederating Lemmy instances from Threads makes even less sense. One of the big Lemmy instances blocks Threads but doesn’t block CSAM instances. Insane priorities their admins have.