Same username cannot be used in more than one developer accounts

Current behavior:

Once a developer account is created with the username "user1", if immediately afterward an attempt is made to create a new developer account using the exact same "user1" as the username, an error below username field appears with the message:

"has already been taken"

Currently, if there is an user provisioning process in place that only utilizes the username (not email based) then it cannot be used other approaches such us multi-emailaddress-values.

Desired behavior:

Be able to create different developer accounts using the same username.

Why the need:

Have to differentiate the application-secrets between (internal) consumer-orgs. But there are developers, which are working for different consumer-orgs at the same time and they have to be able to define application-secrets for more than one consumer-org.