This seems extremely elitist, even if just for the fact that you do not know what other knowledge (and experiences and viewpoints and...) those people who'd be interested in those communities would bring.
If you want a site comprised entirely of - what it seems to me - techbros who talk about how large their homelab Kubernetes clusters are, you should do that by curating your experience with the general platform, not by excluding anyone else, which is what you're doing here even if you don't realize it.
I personally want people from all walks of life to set up shop in the fediverse (as long as they're not jerks). Even if I'll never see or interact with 99% of what they create, maybe that last 1% will solve an obscure problem I encounter, or recommend me something (whether it be a product or recipe or location or...) that will change my life for the better.
I do not agree with the people wanting to control other servers by trying to force defederating from threads. Independent admins running their own server is what the Fediverse is built upon.
As long as authorized fetch is implemented (and correctly), intermediaries can't "leak" messages out anyways. If Threads wanted to read the contents of a boost, they would have to ask your server for that, and your server can tell them to screw off.
Does kbin or Lemmy implement authorized fetch? If they don't they should start working on it. And consider enabling it by default. I know versions of Lemmy >= 0.18 can talk to GTS (which enforces AF) so there is partial support for it. And nobody runs 0.17 because of how inefficient it is, so that won't be too big of a backwards incompatibility issue. No idea how it works on kbin land here, but it should be implemented ASAP if only so that any future enforcement won't break backwards compatibility.