In the hopper means something is in preparation or is on its way. When something is in the hopper, it is going through the last refinements before it is ready to begin or to be presented.
A hopper is part of an agricultural or industrial machine that is a sorting device, for separating things such as grain from chaff, or gold or other precious gems and minerals from mud and rock. The hopper shakes, allowing the undesired matrix to fall away and leave behind the coveted grain or mineral. The term in the hopper derives from the word hoper, an English word first seen in 1277, designating the hopper in a mill that processed grain.
In the hopper was a more popular phrase from around 1910 to about 1970, according to Google Ngram. Its use has fallen considerably in the last twenty years.
The Chiefs had all of their runs in the hopper by the fifth inning, thanks to two key hits by Trimpey and one by Zane Morgan. (Gant Daily)
The vast majority of product development teams are under resourced, overtaxed, and constantly bombarded by changes to existing product developments as well as revisions to priorities for projects already in the hopper. (Namibia Economist)
Nationally, Chicago and Seattle were among cities raising their minimum wages last year, while such municipalities as Washington, D.C., New York City and Portland, Maine, have wage-boost proposals in the hopper. (The Los Angeles Times)
Gun safety groups and the gun lobby each have bills in the hopper, and offensive and defensive playbooks ready to go. (USA Today)