I'm looking for examples of new software from the past (contemporarily: AI, Blockchain) upon which entire companies (and a new category) were going to be built, but ended up absorbed by real companies in real sectors?

We currently have a "Blockchain sector" in tech, with "Blockchain companies" . But that's not a real sector. The Blockchain itself not a platform, it's a tool.( Ditto AI).

What will exist will be cloud storage/database companies specializing in using the Blockchain in specific existing categories: Fintech (global remittance), Permanent digital archiving etc. It's like how Telegram isn't a "Mobile Apps" company, it's an information transfer (aka communication) company which competes with SMS, newspapers, physical human going to a place to deliver the message by word of mouth etc.

So yeah, what are examples of this happening in the past? "New software" at first births "new software" companies in the "new software" sector, until, eventually, "new software" becomes just a normal tool, not with its own companies in its own sector, but which enables companies in existing sectors.