To ask for this feature feels like an overreach but I thought I would mention it as you continue to evolve our relationship with the front matter.
Tumblr cross-posting (from the JSON feed) works great. So far I just touch up things like source content, tags, and those videos Hugo continues to deny the existence of.
One assumes such APIs would allow for setting the first two when cross-posting. Some form of hidden (think the use of
<!--more--> when I say hidden) API for configuring such data for cross-posting to specific platforms would be wicked cool. Or perhaps, if front matter access is in our future, an API that makes use of custom parameters or whatever.