Only just discovered stringify and I already like it a lot more than IFTTT.
One observation I have in migrating some of my recipes over is that the stringify notification currently shows the name of my flow as well as the text I enter into the notification.
This seems a bit too techy for the purposes of push notifications, which I see as user-friendly messages rather than debug information (which is provided by the logs in any case). For example, my wife has no interest in which flow just ran (or indeed what a 'flow' is), only that Nest was now in 'away' mode. Would you consider just having the "Flow: " line as the default entry for the user to choose to include or overwrite?
IFTTT notifications have a 'rich' mode, where notifications can be enhanced with additional detail, including links to apps and URLs (which depending on how security conscious you are, may or may not be a good thing). Would simple/rich notifications be something you could also consider in the longer term?