The reason it "doesn't make sense" for such a functionality is because basically you would "filter" through ALL products in the shop, no category being chosen by the customer, no product - this makes it more complicated AND additionally, depending on your theme a corresponding block might not be available. We will be implementing this function in our LiveFilter but currently we need more use cases like yours to have a better idea of the use case.
One useful info would be:
What theme are you using and does it use column layout on the homepage?