We already had a zombie day that was mostly hated by everyone
I honestly enjoyed the day with some exceptions like camping at the top of climb or really hard to reach places. We have already discussed new possible days and our devs are working on it.
edit: if you're wanting a day that's like HnS but the other way around, call a reverse HnS day: CT's hide and T's seek. CT's can't knife back (how I play it, you can change it to CT's can knife if you want) and T's are allowed to kill the CT's however they want.