To be honest, sales aren't going to help. It might start a short influx for a bit but that's about it. Plus, the majority of people who buy games during the sales just buy it because it's cheap, but either never ever play it, or play it briefly. And with NW being a DLC, a lot of people will overlook playing it entirely.
YouTubers are definitely the biggest influx. It's one of those games that once you see gameplay, you know you have to play it, and next thing you know, you're leading a regiment. lul. #mystory #realtalk
Anyway, getting good YouTubers into the game is a good idea. Just a couple LPers to make one vid each, and that's already a major increase in players. It also demands the regiments of the community to recruit, otherwise people will play, and people will go.
I've always thought a collaboration channel of some of the most charismatic, funny, and entertaining community members, with the support of the rest of the community (YouTube works so that big YouTubers get bigger) would eventually get people attracted to the game long term. As long as these people don't directly advertise regiments and stuff (just for it being unfair), it would benefit everyone.