Hi,
It's not impossible but really hard to do. That's why we never got around it.
The problem is that filters have to take into account many things. Add the count on each choice will require running a MySQL query for each choice of each filter. This will drastically slow down the processing on websites with lots of filters/products.
Also, we can't do that as an override. If we work on it for you, we have to develop it directly into HikaShop as it requires modifying the core files handling the filters in HikaShop. That also means we can't cut corners. So it would cost 600€