To post to more than one sub at a time just use commas in the sub field.

This will create more than one post. The front page will only show one of the instances, but /new will show all of them to make it easy to verify.

I tested it with these two posts:
https://matrix.gvid.tv/c/Music/5jScgGXEZ9
https://matrix.gvid.tv/c/Techno/9FvAQPAPfL

Outcome:
Front page: https://matrix.gvid.tv
New page: https://matrix.gvid.tv/new

Depending on how people vote the posts will compete with each other for which will be seen on the front page.

Reposting content here to additional subs is encouraged. This only works with link posts. This helps fill out some of the obvious topics people might try to visit.

Ideas for a second round of follow up features that might happen:

• Make a repost button on posts to encourage more reposting and filling out of topics.
• Make it so reposts where another is within a certain age will have some initial age added to them to make it harder to slide a developed discussion with a new repost.
• Change the way I do all caching internally to make it easier to do these things with less shimmy code. map.js manages mappings between many object types with a LRU cache for all mappings. (more internal than an outward feature).
• Publish a list of subs I've seen traffic go to that have zero or near zero content