I think it would need to be a mechanism similar to how user moves are handled where the old thing sticks around forever but has a field that says “the new one is over here” and then the new one has a field that says “yes, I am the same as that old one”. At least I think that’s how e.g. mastodon handles moves of users (just the person/actor, not any of their content. AFAIK nothing in the fediverse can do something like this with anything other than a person/actor at the moment)

The problem is the thing has already been federated. Changing the ID in the db will appear to the rest of the fediverse as new things, not as those same things.

I would still go with one that isn’t one of the biggest. My general advice is to find one that fits the vibe you’re going for, communities you’re interested in (e.g. some are focused on art or cybersecurity, etc), or is somehow tied to your locality. It shouldn’t matter that much, though some servers will be a little more (or less) strict with things like federation, content warnings, alt text, etc. Usually the server will have some info telling you some of this, and their admin should be linked and likely has a post or two pinned to their profile explaining some of this as well.

I am partial to kind.social, though have opted to run my own instead of joining up anywhere.

I know that is an often discussed and requested feature, but as of right now there is no import/export as far as I am aware.

It can cause some wackiness… basically you will need to maintain that old domain forever and everything will still refer to that old domain.

For example, your post looks like this from an ActivityPub/federation perspective:

{
    [...]
    "id": "https://atosoul.zapto.org/post/24325",
    "attributedTo": "https://atosoul.zapto.org/u/Soullioness",
    [...]
    "content": "<p>I'm curious if I can migrate my instance (a single user) to a different domain? Right now I'm on a free DNS from no-ip but I might get a prettier paid domain name sometime.</p>\n",
}

The post itself has an ID that references your domain, and the the attributedTo points to your user which also references your domain. AFAIK there is no reasonable way to update/change this. IDs are forever.

It would also break all of the subscriptions for an existing instance, as the subscriptions are all set to deliver to that old domain.

IMO your best bet would be to start a new instance on the new domain, update your profile on the old one saying that your user is now @Soullioness@newinstance.whatever and maintain that old server in a read-only manner for as long as you can bear.

Users are empowered to set what they want their default homepage view to be (“Subscribed” , “All”, or “Local”). I am unsure what the default is, but mine is set to “Subscribed” which I think it makes the most sense for most users.

Unless you are on a heavily moderated/defederated server (such as beehaw) whose moderation policies, politics, etc. you are aligned with it is very likely that “All” is going to contain something that someone doesn’t like. I am personally not in favor of over-policing what users do outside the confines of their home instance, it’s a fine line that I haven’t had to define too clearly yet so perhaps my thoughts here will change.

If you don’t like what’s in “Local”, then to me that is a sign that the instance isn’t for you. Local is a reflection of the sort of content that users on that instance want to see more of. The admin allowing such content is not necessarily an endorsement (unless they were the one to actually post it), but is tacit acceptance of that content and the community that content exists in.

I think some way to make a “Curated” feed of posts only from certain approved communities would be a welcome feature and present a useful middle ground allowing for a moderatable discovery experience, like the default subscriptions provided on that other site.