After talking to Atlassian support it appears that there are no requests regarding using outside SSO providers (i.e.: OKTA, Ping Identity, One Login..) with Atlassian ID.

Is it anywhere on the roadmap to allow the use of existing SSO providers to work with BitBucket by going through Atlassian ID?

It's very possible that Atlassian has already planned of how the thousands of companies that already have an SSO solution are going to use Atlassian Cloud products. I just can't find any information about it.

Our use case:
We would like to begin using BitBucket but don't want to take on the overhead of yet another location to manage users.

We already have OKTA in use for all our major apps (including on-premise JIRA/Confluence) and have no interest in migrating to Atlassian ID for the sole purpose of being able to use SSO with BitBucket.