I think I figured it out well enough for basic functionality. Not optimal, but it seems to work.
If anyone else is using nodebb-plugin-ns-embed, you can possibly use the following rule to get streamable vid embedding to work.
\ watch
\ https://streamable.com/(.*)
\ replace
\ <a href style=""><iframe width="1024" height="520" src="https://streamable.com/s/$1" frameborder="0" \ allowfullscreen></iframe></a>
