I don't think a counter to show how many days the food in the pen will last would be a good idea, for one reason only - it's dependent upon how many pets are on your profile, and the current hunger level of those pets. Those are variables that can change at a moment's notice and would probably cause quite a bit of confusion and upset if someone had one pet out and assumed the food would last 100 days, emptied out 30 pages of pets from their showroom, then didn't log in again for 3 months o______o (not a reasonable assumption but hey I can see it happening).
A counter to show the number of points the food in the pen has though, that's a lot safer I think. Plus we need points brought back anyway. Not sure why that went away in the first place, it was really convenient... >(
tl;dr - support for an alert and food points counter. no support for how many days food in the pen will last.