If you start a company and spend a non-trivial amount of your time, effort and money into handcrafting and customizing a perfect IRC server, that company is going nowhere.
If you know IRC well enough to want to mandate it for your company, you can probably set the server up in an hour or three. You can then install https://thelounge.chat/ and have your employees log into that for browser and mobile apps vs. native IRC clients.
What money would it require? Any leftover PC from the last 15 years can run the server.
Aggressive delegation to third parties is how we end up with all these complex services. A chat system, a ticket service, a git interface, should be pretty trivial to install and maintain. And consistent too.
Worked at Red Hat, the amount of anger around decommissioning our internal IRC servers was HUGE (and hell, even then, half the company was using/happy with GChat, the other half on Slack. People who actually paid attention to both were very minority).
Loved having IRC at Red Hat from a nostalgia perspective but it was a total disaster from a business standpoint.
Also, at red hat, we’d complain to the whole company about paper towels vs air dryers in the bathrooms, so naturally the complaints about losing IRC would be expected! It’s refreshing to be at a place where I can make a decision without getting second guessed and derailed by someone totally unrelated to what I’m doing.