As the self proclaimed best Dark Ranger RPer on the realm (lol), I can safely say there are still plenty of things you can do with a Dark Ranger character. It can be as simple as now following Velonara and the Horde, or staying loyal to Sylvanas as they try to undermine everyone. It’s up to you to decide how much would your Dark Ranger character know about the Shadowlands. They can also seek reaproachment with the Blood Elves, or keep acting as guides to the Forsaken, the latter being harder since the Forsaken are so split right now. There is also the matter of RPing a night elf Dark Ranger which opens some interesting avenues for conflict. Lastly, there is always the Calia angle you could try, but the lack of lore around that ‘character’ might make it a bit more difficult.
Personally, I think the elite spy aspect of them makes them ideal for exploring all the things I’ve mentioned above.
The biggest downside of Dark Ranger RP is by far the social RP side, as they are, for lack of a better term, very edgy. While in combat they have a pretty well defined set of skills they can employ, when the fighting is over the limitations start to creep in. There are work arounds and by no means you should just stay brooding in a corner, but it is for sure harder then most concepts.
Also, we’re recruiting, so all cool Dark Rangers should join us