Hey, thanks for bringing this up. I completely agree that this is indeed something that we should discuss as a community. I haven't had the chance to make a thread about this yet, so we'll use this one :)
I have been keeping an eye on the de-federation of some instances but afaict the primary reason they did that was because of the open signup nature of those instances resulting in a flood of potential bot/troll accounts which the mods couldn't keep up with (understandably so). LemmyRS is (and probably will be in the foreseeable future) an application only instance. We just don't currently have the infrastructure or the manpower to deal with a completely open instance.
Any user who signs up using this instance presumably understands the target topic is Rust (and we have communities on this instance to cater to those users, so it's already pretty self-isolated in that sense). If someone wants to subscribe to communities on other federated instances they're completely open to do so. While things settle I think this approach should serve us well (please feel free to disagree and provide any counter arguments).
But again this isn't my unilateral decision, I would simply do what the users of this instance want as a group.