The workspace_id you want is taken. You visit the account profile and see no account activity, can you claim that account? No, you can't. And this is why...
Bitbucket offers unlimited free private repositories. Many users take advantage of these free repositories. These users create an account and work 100% on private repositories in their workspace. When users work like this, you can visit their profile pages and you may not see any activity for them. As a matter of fact, you may only see that they've signed up. Yet these users are hard at work in stealth mode.
Additionally, Bitbucket allow users to choose their own workspace_id. The first person to choose a workspace_id gets it. We won't ever give away another user's chosen workspace_id. It is theirs to keep for as long as their account exists.
In short, the answer is 'no'. We won't give away another user's account for any reason.