It's fixed! The beta patch for next week has been updated to include a fix for the mac black screen: https://forums.obsidian.net/topic/98361-fixes-to-the-patch-beta-build-71/
Here is the reddit thread for instructions on how to access the beta patch: https://www.reddit.com/r/projecteternity/comments/8iqfja/patch_beta_is_on/
I can confirm, it took me 10 seconds to download and apply the patch and I now get past the intro! have a late 2015 Macbook pro with iris 1536mb graphics, a little laggy but playable. See you all in Eora.