PHP evaluation

I agree. Funny, I actually mentioned this in your other post #1448050: Condition to query before and after value on form element change. I would love to look at adding php evaluation in Rules Forms conditions and actions that allows advanced users access to existing form values or to form elements. There will undoubtedly be a lot of obscure feature requests as this module's popularity increases, and I'd prefer to offer an avenue for implementing those obscure requests without unnecessarily crowding the core conditions and actions. For the most part, the core conditions and actions should be targeted to users without the skill or time to implement hook_form_alter() in custom modules, and providing some custom php code integration should suffice to cover the users that don't fit that description. A little code sharing in the issue queue can take care of those obscure feature requests if the php processing support is properly done.

You can use the rules php_eval action and condition for this already. The variables exposed by the rules_forms events are available for you to use:
$form, $form_state and $entity