While I haven't received any official information about this, I believe that historically, you can purchase an upgrade for either platform - it doesn't need to be the same platform as your older version. If I am able to find out more solid information, I'll share it.
edit: Actually, I re-read your message and now I'm not quite clear what you were asking about. Generally, Adobe offers a free update if a version of the software was purchased sometime after the announce date of the next release. For example, if Adobe announced the next version of Photoshop would be released in January, and you were to purchase the current version in December, you would usually be eligible to upgrade to the new edition at no charge. This isn't always the case, but is pretty common. Again, as soon as official pricing and upgrade information is released, I'll be certain to share it in this forum.
If I were to buy a copy of Audition for Windows would I be eligible for a free cross-grade to MAC?
More specifically I work in Education and we have a small pot of funds which may be taken with pending cuts. Could we buy Audition and use the Beta until the full Mac version is released?
Apologies for the confusion
In regards to your question on using the beta version, you are welcome to use it for whatever work you see fit, however keep in mind it is beta software and it will expire at a future date when the retail version is released.
As for the *free* cross-grade question, like durin noted we do not have answer on that at this time but will be happy to share once we know more.
Sr. Program Manager - Audio