People interested in BitChat should download it just so you have it in case it gets popular or you find someone to use it with. I tested it and it's surreal to text without WiFi or cellular.
Even nesting geohashes would be cool, though I think the concern is the chaos that happens when you see half a conversation but not the other (as with radio when one party is in range but the other is out). The fact is that geohashes as it is get basically down to the level of acre or so which is just a wildly precise level of granularity (though might be useful if you had a whole 12 story college dorm building all in a chat or something).
It could do with a UI tweak though so that by default it shows you the most 'zoomed in' geohash with any activity.
IRDA is 1-to-1 and basically requires both users to do nothing else but use IRDA (including being within line-of-sight of each other). For a use case like talking to a family member a few seats over on a plane, IRDA won't help you.
Bitchat, at least in principle, doesn't require you to sacrifice the entirety of your phone to constantly run Bitchat in the foreground, and can work over larger distances (and with a mesh architecture which lets you reach people that you wouldn't normally be able to reach).
Writing an app that has the equivalent of 2000s-era functionality is a day of work at most. You don't even need to, you can achieve similar objectives via Airdrop / hotspot names (the latter being used as a loophole to communicate across prison cells). This is not what Bitchat is.
Who would advance it? Can you even get multiple parties to agree on what's in it? Is there any identity required? What's there to stop this being another "Bluejacking" vector but now with dick pics?
Given all of the above the proprietary route seems inevitable, even for protocols over Bluetooth.
AFAIK, they changed policy a few years ago, so that even if you set discoverability to "everybody", it changes back to "contacts only" after a few minutes.
There seems to be somewhat of an upswing lately though. Federation is cool again, and many of the implementations active now seem much more stable, instead of weird half-research projects that killed themselves by ignoring the real world too much (which was sometimes true to their goals, which is fine but unfortunate).
FireChat was released in 2014.
I have a vague memory of sitting in school in like 2006 or 2007 and sending messages via Bluetooth to a classmate on my Sony Ericsson K750i.