Yep.
Technically Nostr.build or other Nostr upload services could support custom domains too. They would just need a way to link a domain to a pubkey, and redirect the cdn.custom.com requests. If you use HTTP AUTH for uploading, it could be as simple as just select provider in the app drop down - once domain was verified/configured in some web portal.
The goal being if you used them and then moved away in future, as long as the file paths don’t change, you can just download and upload to a new provider. URLs won’t break.