While not as flexible as tags, what you can do right now is put the same plug-in into multiple collection folders. So for example I have all my plugs arranged by both function (Dynamics, EQ, Modulation, etc.) and by vendor. Also all my Compressors are in my Dynamics folder, but there is also a sub-folder for compressors with Mix controls. So if a compressor has a mix control it will be in my main collection 3 times - once each in the 1) Dynamics folder 2) Mix Control sub-folder & 3) Vendor folder.
Basically I think the key is to have your collection(s) reflect the various ways you think about the plugs.