Damn - every single thing I hear about it is so cool. And in fact I did think about whether you would want to host some kind of AskUSA/CasualUSA there (and then to offer my help modding it - like you, not wanting to be the head but to donate a bit of time if it would help), but figured (1) if you had wanted to then you would have initiated such by now, with all of the people talking about such, and (2) then I saw your statement that "While we're not quite ready to throw open the doors (we're still configured as a regional instance)...", and wanted to respect that.
Speaking of regional there is also an !askmidwest@midwest.social, which despite seeming to be mostly dead (the last post was 4 months ago and the one before that was 8 months ago), is likewise not quite the same as a truly, fully national community. Not that any of this is bad ofc - there are communities across the Fediverse for specific regions, states, provinces, even cities, and likewise for specific show series (hehe Star Trek:-P), individual games, etc. as well as entire genres and sub-genres of such. Though there does seem a need for a truly, fully USA-wide community as well, if only to help attract good content creator-type people (e.g. comic artists) from Reddit or the failing X over to here, who may be part of a region that is not yet served.
So Discuss.Online can help there - like dubvee.org it even lacks the name "Lemmy" that can conjure up thoughts of the tankie origins of the software (a saga that many Redditors are familiar with - I at first strongly hesitated to join it myself, though then went with Kbin back when that was a thing:-D), and is a fully general instance, not only for the USA but it is based here. And to help promote the instance it also helps to have such a community here:-).
You are right of course. On the other hand, the developers are working slowly on other issues and do not seem to have made this one a priority. And Rust is reputedly an exceedingly difficult language to learn to program in, even for someone who already knows C++. I expect PieFed (Python) and Sublinks (if still active, Java) to quickly surpass it with features, though Lemmy definitely has the edge in terms of most effort put into it so far.
On the other hand, we are still at version 0.19.7 - so definitely still a beta software rather than a fully functional one? Plus it's not meant for profit, so we make do with fewer features, and have only a very tiny set of developers working - those that can be supported by grants and donations.
Plus the entire thinking about how things should work seems to keep changing? Like, the original federation model was not built around the idea that Lemmy.World would have ~80% of all Lemmy users on it - and yet on the other hand, moderation tools, especially across instances, suck absolute ass (reportedly), so the entire Fediverse is kinda really struggling right now, and niceties such as this simply don't get worked on until the more major foundational issues get laid down. Fortunately new communities don't get created every day:-).