Theory: The grey goo’s hunger can actually be satisfied
The evidence actually lies within the achievements of back for seconds, specifically the eating milestones. The namings of these achievements go from “peckish“ to “hungry” then “starving“ and then “ravenous“ and on to “could eat a horse” while having the icons show the grey goo eating progressively larger amounts of food in the respective order (with the exception of “could eat a horse” wich just shows the grey goo about to eat a horse as a nod to the idiom) and you might think that this contradicts my overall point, but the last achievement in back for seconds for eating a certain amount of objects after “could eat a horse” is titled “stuffed”, with the icon of that achievement showing the grey goo NOT eating, looking to have just engorged itself on massive amounts of food and looking perfectly happy and satisfied with its meal. Considering how the word “stuffed” in a term of hunger means completely full and unable to eat more (wich I do assume you know) the meaning created by this achievement directly contradicts the other eating milestone achievements and implies that there is in fact a limit to the grey goo’s seemingly insatiable appetite. (You can find the achievements I am talking about in this link: https://steamdb.info/app/445110/stats/ )