Comment by stickfigure

Depending on how fast you can execute it may be too late, but right now you have a brief window of opportunity to get a seedbed of users.

Reproduce the Reddit API exactly such that these soon-to-be-defunct client apps can work with minimal changes (ideally, just a configurable root domain). Reach out to the client authors and see if they will enable your site. Maybe you'll capture some of those user communities.