Edit: this issue regards Hajk's vector layers, which is the layer type that currently supports some CQL functionality.

Edit 2: I (@jacobwod) just realised that this is related to #498. This new functionality should produce a filter that looks the same and is written to the same f parameter as #498. Note however that #498 is about WMS layers. This issue was originally about WFS/GML (Hajk's vector) layers. So what shall we do?

The ability to filter on several attributes and not just on one as it is now. This would mean that many times you could avoid publishing the same layer several times in geoserver / Hajk admin.

You set predefined filters for the layer in admin that the user can then use. Dropdown lists that filter what the user selected.