First off, many many thanks to @jimzarkadas ! He suggested this on our 1-1 call.
For so long, I've been reluctant to ask for user's email when the user would start the app for the first time - since I was afraid users would simply close the app and leave it at that.
So, @jimzarkadas suggested I add a welcome screen, and ask for the email there. I created the welcome screen inspired by iMovie (also, per Jim's suggestion :D) We expected roughly 20-30% of users would leave their email.
And lo and behold - while I don't yet have exact data, by doing some calculations, so far, it's in the 65-70% range (15 subscribers, in roughly 16 hours).
A bit more info:
I did make the subscribers a promise (see below), and clearly, I intend to keep it. All in all, more than happy with the result!