Another feature included in ‌iCloud‌+ that wasn't discussed in the keynote is the ability to create a custom email domain name.

Personalize your ‌iCloud‌ Mail address with a custom domain name, and invite family members to use the same domain with their ‌iCloud‌ Mail accounts.

In essence, what this means is that when ‌iCloud‌+ goes live, Apple will allow users to change their ‌iCloud‌ Mail address completely.

Additionally, Apple will allow users to invite family members to use the same domain name with their own ‌iCloud‌ Mail accounts, although it's not currently clear if family members will need to be part of Family Sharing for this to work.

It remains to be seen whether custom email domains for ‌iCloud‌ Mail will have certain limitations that rivals don't set, though.