The system here meets the minimum for Joomla 3.x (PHP version is 5.3.25 with the RHEL crypto patch, MySQL version is 5.1.68 and while the server engine is LiteSpeed, it's compatible with the required Apache version) so manual installation shouldn't be a problem. That said, dot-0 releases of anything are generally (and wisely) regarded with a lot of skepticism by anyone who might assume liability for supporting it, and Joomla 3.1 is a relatively recent release (April). Add to that the cautious upgrade cycle here (fixing things what ain't broke often means that they will be), and you can be pretty certain that there'll be some lag before it's added. But there's no technical reason why it can't be, just logistical reasons. If you're comfortable with a manual installation, you should have no problems.