According to an email just received:

"Keys will replace Qcredits and unlock availability to the award flights and upgrades of your choice. This will give you the chance to spend Avios on award flights to remarkable destinations, or upgrades to indulge in ultimate luxury.*

Your current Qcredits balance will be automatically converted into Keys soon. You will receive two Keys for every year that you renew your Platinum tier"

No sign of the *T&Cs, but if this means 2 guaranteed upgrades and/or standard rate redemptions per year that is a positive enhancement for me!