I see literally no reason to add these at all, nor do I for the linked .svelete and .vue PRs. The "reason" given in the other PR's doesn't make any sense.

See #445 (comment)

According to @OliverSpeir's Discord response, it should be text/plain instead

But that’s not the official MIME type. We were just discussing which one would be the most appropriate if that were the case. In any case, this would only matter if that Astro file were being sent over the internet,but those files aren’t meant to be served over the internet, or am I mistaken?

It would be better to reach a consensus within Astro, since that was only the opinion of one Astro contributor and doesn’t represent the whole project. So the best approach would be to open an issue so everyone can agree on it, and either register it through IANA or clearly document which MIME type should be considered the reliable source.

this would only matter if that Astro file were being sent over the internet

In a project I'm working on, we enable people to sent .astro (and .svelte & .vue) files over the internet and we want to do extra things for each one of them

In the meantime, I've opened withastro/docs#13335 so we could wait for an official consensus from their side

Okay, cool, it’s always good to understand the use case. As you know, for anything you want to add, there needs to be an official source. So you’ll need to do the same for the other frameworks as well.