Adminer is declared as Beta in version.php, and it has drawbacks:

• (by default) new versions are not discovered by ad-hoc task
• even with admin manually searching if new version exists, you're not notified (and can't use automatic update)

I feel it's a problem, because most people will not be aware of new versions, and will stay to old ones (only admin having declared they want to be notified about beta version will see everything.)

Apart if there really is a good reason, i feel you'd better declare it as stable.