But that doesnt affect the rarity during the expansion itself. During MoP (which this should try to emulate) you also always had the chance to get them, yet they still were rare. The CMs dont get easier over time, so the challenge always stays the same (ideally).
However, it does get easier over time, when something (going to use ICC for instance) the Raid has been out for a long time a lot longer than CM obviously but with everyone (who should know how ICC Mechanic work by now) it will be easier cause you know what to do. Apply that to CM it will still allow everyone and everyone to get the gear. On top of that, if a guild has it on farm (Saw this in WoD mind you considering in MoP my account was Wrath Level) they can allow people to buy a carry from them.