Discord's main problem for me is that it's built around people having one and only one user, which is a huge privacy and pseudonymity mess. The only alternative that works somewhat is using the PTB version of Discord for your "alts".

If this project has genuinely decent multi-user support instead of the miserable experience of Discord, I'd emphasize and promote that first over being a Discord-like, since this genuinely improves on some of the privacy issues of Discord, despite AT Proto being public.

Better to distinguish the product from Discord rather than promoting how similar it is. Because of the public architecture, it's more similar to a forum board than Discord anyway, so you could also just as well give people another interface by showing the community as a conventional website. People may or may not like it, but it's basically what it practically is.

One of the big issues with Discord is that it takes public knowledge like wikis and makes it private instead - and beholden to the whims of mercurial mods and admins. Information being public doesn't have to be a bad thing that way.

Instead of Discord, you can give the people Discourse. :)

tl;dr: AT Proto being "open" can look like a bad thing in nominally private spaces like Discord, so promoting as something more open like an open forum board rather than a closed Discord server might be more interesting and persuasive. But I'm also a forum board evangelist.