Maybe I just have the wrong definition of accessibility.
To me IRC is far more accessible than any of the proprietary services, because it's an open protocol. It allows me to pick the client that is most accessible _to me_.
And your needs may be different than mine.
Don't want users having to install their own client? Host a matrix/thelounge like service, which gives you the best of both worlds.
You can use your own client or this service then. How does it get any more accessible than that?