Were you personally wounded when Google declared that Inbox would no longer include 'Someday' among its list of Snooze options? It's likely you weren't alone. The latest update to Inbox doesn't appear to bring back the recently removed feature, but a couple lines from a teardown suggest it might be coming back.
The features discussed below are probably not live yet, or may only be live for a small percentage of users. Unless stated otherwise, don't expect to see these features if you install the apk. All screenshots and images are real unless otherwise stated, and images are only altered to remove personal information.
It was just two months ago that a post in the Google Product Forums declared that the Someday feature was to be retired. However, several short forum threads and probably a more significant number of feedback messages about the removed feature may have swayed the Gmail team to bring back this ultimate feature for the unmotivated among us.
When Someday was pulled in the update from v1.72 to v1.75, only two lines were removed. Those two lines are back as of v1.76, and not much more needs to be said about that.
Actually, there is one point to be made here. As likely as it is that Someday is coming back, I have seen a few instances in the past where text was removed from an app and then returned for a short time, then disappeared again. I can only assume this was due to restoring a piece of deleted code from version control, and it also brought back more than was intended as a side effect. In other words, there's some chance this happened by accident.
And just in case you're reading this and wondering what all of this Someday business is all about, it was simply an option to move email into the Snoozed folder without attaching a time or date for it to be restored to the inbox. In other words, it was a way to indefinitely hide an email from view without marking it complete, but leaving it in a place where it could be easily found later...assuming you didn't use it too much.
The APK is signed by Google and upgrades your existing app. The cryptographic signature guarantees that the file is safe to install and was not tampered with in any way. Rather than wait for Google to push this download to your devices, which can take days, download and install it just like any other APK.