AFAIK, the only thing that might break is the RTL feature. That will result in notices in your error_log. In order to fix that you can force a value to the field. In order to do so, in the qa-theme.php file add this line:
private $isRTL = false;
class qa_html_theme extends qa_html_theme_base
If you want RTL support then use true instead of false.
Then you'll also have to change this line:
parent::__construct($template, $content, $rooturl, $request, $textdir);
With this one:
parent::__construct($template, $content, $rooturl, $request);
Note this applies for beta-2. I'm pretty sure the latter change shouldn't be necessary for 1.7. The RTL one should still be needed.
You will need PHP5 too to handle the new constructor but I guess you already fulfill that requirement.
Anyway, giving it a try shouldn't break anything. Even if it does break the whole theming and makes your Q2A installation unusable from the UI just remove the SnowFlat directory from the themes and that will default it to the Classic theme :)