Advanced reminders are going to be a thing for the next big release. I agree that one problem is to pass the unlock, but staying on track with your intention is a different story. One periodical notification with static text can in theory fix that, but the chances are low in comparison to the full-screen pop-up. I intentionally focused on the unlock procedure first. For now, you can combine it with other apps like minimalistic launchers and apps that pop up after the app opens. But eventually, improving the reminder experience can make the solution more complete, I agree.
About typing "captcha" or random characters. I think it's just a different type of nudge. Another can be a small mini-game to play like catching a moving object. I'm going to consider adding different types of nudges to the app. Thanks for the suggestion.