The developers have announced they will start advertising the game via a few YouTubers. I decided I would calculate how successful that campaign may be. First off let's make a few assumptions for our calculations -Thrive has around 3000 people monitoring it's progress to any degree -there are about 15 developers working on the project -about 10000 people will monitor Thrive's progress after ad campaign (quite humble considering subscriber count)
15/3000=0.005 gives us the number of developers per follower 0.005*10000=50 possible newcoming developers after advertisements 50+15=65 developers in all
Note: Getting 65 developers in all would be difficult to manage KSP only had around 20 devs when update 0.19 came out
Your numbers might be overestimates. We have ~10 active to semi-active developers, but at the same time I wouldn't say we have 3000 proper followers. I doubt most of the subreddit subscribers care much for us. I'd estimate this is somewhere in the region of 1500. The dev to fan ratio is therefore slightly higher than your estimate at 0.0067.
Scott Manley (by far the largest potential YouTuber we've had interest from) gets on average 20000 views a video. For something unknown like Thrive, I'll be conservative and say it'll be around 12000. Of those, I think only 10% or so would continue to follow Thrive, giving 1200 new fans.
DarkEdgeTV gets about 5000 views per video, though it'll be something completely different to her usual style so it's impossible to know whether this number will be higher or lower than usual. Applying the same 10% gives 500 new fans.
(1200 + 500) * 0.0067 = 11 new developers
Yeah, this is massively smaller than your estimate, but it's taking the most conservative values at each stage. Plus, even one new developer can make a massive difference - we'd probably still be stuck in 0.2.4 without TheCreator.
Anyway, these are just estimates. Who knows how many new devs we could gain?
Yes but it also depends on what kind of video is made. Xcom only gets about 1000 to 3000 views on Scott's channel. But new videos in a series, or anything new for that matter score much higher in view count. They can range anything from around 100,000 to 1,000,000 (1 million is highly unlikely for Thrive but it has been hit by a few new videos for Eve online). Something similar goes for Dark Edge TV. If she starts doing something a bit different with her Spore creations, the view count rises for than an average video. An average does not account for the outliers Regardless of what these numbers come out as, you will still have a large amount of newcoming developers.
One final thing to note is the domino effect. Once other channels see what another channel has done, they will likely make a video on the same topic. Nerd cubed, Jacksepticeye, and Danny2462 have all at one time or another mentioned they have watched Scott's videos. I image the same goes for Dark Edge TV.