Caffeine countdown & Food group servings
From the health coach side of me, I'd love to see if a caffeine 'countdown' would be a viable option. Yes, I know that there are factors that impact it's metabolism, but in general, having a graph or something to show when/how much you have left in your system at any given time would be really helpful. This would be particularly useful for those with sleep troubles, use pre-workout, are breastfeeding, etc. Then people could see the impact of the amount/timing of caffeine intake on their bodies.
The Registered Dietitian in me would really love to see something that would show how many servings from each food group you're getting from the foods you log. I preach balance first, calories next (usually - since my patients aren't even ready for nutrition 101 yet). The USDA food tracker was great for this, but it's been shut down for a few years now and they never had an easy-to-use app. ESHA will do this, but honestly, only professionals use it and I HATED the UI.
Just some far-reaching ideas, I know...BUT they are ideas that no on else seems to have in their apps/sites, so it could be a selling point