What's a Class F cargo compartment?
Here in this amendment to the EASA CS-25 it says on page 4:


  ... for a new Class B cargo
  compartment definition as well as design criteria for a new Class F cargo compartment
  type. This latter class of compartment was introduced because whilst it was concluded
  that manual fire fighting was not feasible for larger compartments, alternatives other
  than just the existing Class C were identified. 


And a bit further on page 5 (emphasis mine) :


  ... Further, a new Class F cargo
  compartment definition is added, which is not limited in size and which provides the
  means to control or extinguish a fire without requiring a crewmember to enter the
  compartment. This proposed Class F compartment standard accommodates the carriage
  of large amounts of baggage and cargo loads on Combi aeroplanes as well as in
  compartments of smaller sizes exceeding the new Class B definition. New aeroplanes
  designs can take advantage from the variable solutions under the Class F definitions to
  ensure an acceptable level of fire protection. 


And more concrete:


  The AMC further provides guidance for usage of other fire
  protection means in the new Class F compartment such as Fire Containment Covers
  (FCC) or Containers rather than having a liner installed to contain a fire and to protect
  the critical systems and structure of the aeroplane. 


I guess it's meant to allow storage of cargo in non-cargo areas (which do not have the adequate fire protection measures such as liners) if other non-traditional measures are installed (such as the Fire Containment Covers)