Yeah. The longer we wait to make this decision as a community, more the cost of merging and the load on lemmy.ml.

Do you know if communities can choose their own custom CSS?

The rust instance can federate with others so users can use the same account everywhere. The OP has an account on programmy.dev, you have one on lemmyrs.org, and I have mine on lemmy.world and yet we are all having a conversation on this thread without issues.

Owning the instance gives admin permissions to whomever is running the server but also the headache of maintaining uptime. If we move this community to programming.dev, the rust community would be “tenants” on a common instance. This option would be a no-brainer for smaller language communities (where my brainfuck enthusiasts at?), but if rust community decides to completely move to Lemmy, it might make sense to have a separate instance.

In terms of raw scaling for Lemmy and pure efficiency, AFAIK, fewer large instances is better than lots of smaller instances that federate with each other.

But the question is less about efficiency and more about trust. I’d rather have this community on programming.dev (first choice) or lemmyrs.org (equally great except for the fragmentation) depending on which admin the community is more comfortable with.