WCS 2.0 does not support vendor CQL_FILTER parameter like WCS 1.0 and 1.1 do

In WCS 1.0 and WCS 1.1 it is possible to add a CQL_FILTER in the request url to filter down structured coverages based on arbitrary logic (going beyond dimension support). WCS 2.0 has all the machinery to do the same, but lacks the one line of code picking the filter from the request.