Can confirm that what I want is Inbox's UI. The ease of postponing items into the "Snoozed" queue, and low-effort addition of task items, are both lacking from the stock GMail app.
Similar effects can be seen in the OTT market. Roku gets new features from Sling, Netflix and the other OTT players first, with Chromecast and Fire TV lagging by months or years, and these 2nd tier players are missing Amazon Prime Video (Chromecast) or YouTube (Fire TV) respectively. It seems much like the music sales market IMO...