First, the two would coincide. There's nothing at this time "destructive" in starting up another m/ethfinance on any kbin instance, or lemmy instance, or anywhere in the fediverse. It would live there just like r/gaming and r/games and r/truegaming do, and users would gravitate toward the community best fitting them.
Okay on closer look I see that the subs are distinguished by being prefixed with the instance name
Threads/comments/external links/posts (in the microblog) are cataloged by any other instance that properly federated and subscribed to the magazine from the point at which a user subscribed.
This is a part I need to understand better. So let's say we have your private instance, what causes it to get mirrored? From this comment it sounds like someone subscribing would cause it to get mirrored but that would be it already exists, otherwise how would they subscribe. Is there some prior action that's needed for it to get picked up?
So, let's say I or someone else signed up over on new kbin server readit.buzz, we'd have to register on readit as a user there, then browse to and subscribe to ethfinance@kbin.social to start bringing over data. I've seen signs that the number of cross-subscribers (inventing this term) on a given instance helps prioritize the speed of syncing.
Do you have time to check if you can impersonate yourself? Aka sign up on an instance where kbin is mirrored using "kbrot" as the username, and posting in the daily thread. If that's possible I think that's a big problem.
Caveats are as you've mentioned before: the data earlier than subscription is not brought over, original media is lost unless re-hosted elsewhere, and perhaps most importantly... the links are erased from time (eg. Google searches) so that archival threads, well, aren't. It's similar to the days of lost phpBB communities and forums in that regard.
Lastly, it is a very easy process to backup and transfer the database. However, because there is at least one step involved there with an admin, we cannot yet call it anywhere near "trustless"
I believe admin Sign-in With Ethereum (via Safe) partially solves this and a VPS company accepting Safe SiWE nearly entirely solves it. But that's a wish and a dream at this point.
You'd still be trusting whoever is the person to actually export/upload. However, this could be solved via github. Create a PR to merge an back, let's say monthly. PRs must be reviewed in order to merge. The reviewers are other mods that export and can confirm parity by confirming hashes before merging.
(Sidenote: what's the old dApp that used to parcel out CPU cycles for tokens, was it Gnosis? Or something else with a G?)
Golem?
So back to your instance, should we be using that instead of using this? Or is there no need since we can export the data and launch our own instance at a later time if needed?