Still love this app. It's a regular launch for me when I want to cut through my emails pretty quickly, but it's not my go-to mail app (that's still Apple's own Mail) because it doesn't handle filing and etc. as seamlessly as it could.
Still and all, it's unique in the field and a great app. I won't call it dead in the water -- the developer did just update it in October 2018 -- but its feature set seems to have stalled and, like a few others, I've not received any feedback on feedback.
FWIW, Eightloops does have a Twitter account, but there's never been any activity. I'll keep checking it, this page, and their site, and hope they continue development -- it's a good app and well worth consideration.