I'm interested to see how this changes commonality. I'm pretty sure it has been said the Commonality System is something to look at at some point. For a ATR it doesn't become much of an issue. All you do is convert the older one's to Cargo and bring newer later models in as your passenger aircraft.
But it does bring up some interest with B707's, DC-8, DC-10's when we all retire those but might move them across as cheap freighters. 3 fleet types becomes a nightmare. I would imagine in the long run with changes and updates to commonality this becomes less of an issue, but for the time being as this feature is introduced, it could prove interesting. But we'll see how this evolves along with everything else in the pipeline.