I would suggest the ability to add custom OEmbed proxy server. Actually latest mattermost code is using hardcoded noembed (see https://github.com/mattermost/platform/blob/bb69e98631b2541954b6ae465b8ba5f788b9dc49/webapp/components/post_view/components/post_attachment_oembed.jsx#L33).
Why do I want to customize url?
- When company proxy or firewall block noembed and use your own hosted noembed
- When noembed is KO
- When noembed not support some providers (like spotify https://github.com/leedo/noembed/issues/79) and use your own fork or alternative solutions like iframely (opensource), embedly (maybe not support it in first place because depends on auth/credentials) or custom
Feature will be relatively simple to develop -> just create a configuration and use it.