I'm sure there was some kind of tool to share screens, maybe back to X11? IRC was used in the 90's to let people chat in 10+ groups. I can't remember all the unix-y things that floated about to network, nor all that Sun helped create. Nor can I remember whether IBM (Lotus Notes) or DEC had tools in the 80's. And I'm too lazy to google for it.
Given the clever nature of the HN community and the desire for VC money to make more money, there would have been a lashup in 3-6 months and a product in less than a year to scratch the itch. Y Combinator, of course, would have funded it.
I remember IRC and other Athena tools (Zephyr?) but not anything for screen sharing.
I still suspect you are right though the widespread adoption of Zoom was much easier due to its almost decade long usage and enterprise features like SSO, etc.
Here's one: https://thoughtsofanidlemind.com/2012/12/14/vax-notes/
Our field has no memory of its past: https://en.wikipedia.org/wiki/PLATO_(computer_system)
And people got bored back then, or wanted to hack new things: https://en.wikipedia.org/wiki/Trojan_Room_coffee_pot
NSFW, Jennicam: https://en.wikipedia.org/wiki/Jennifer_Ringley
Given the clever nature of the HN community and the desire for VC money to make more money, there would have been a lashup in 3-6 months and a product in less than a year to scratch the itch. Y Combinator, of course, would have funded it.