I suggest making AdBlock undetectable by websites if that's not against the law. Many websites are fighting back by disabling features or denying access altogether when they detect AdBlock!
Determining that a page is using anti-adblock techniques is about as undecidable (in general) as counteracting those techniques; I can, however, imagine testing for common pre-packaged solutions like BlockAdBlock and warning about that.
Since it seems unlikely that they will be able to build in a way to be undetectable and even if they did it wouldn't last how about an option that would tell you when you were going to one of the sites that did this and let you choose not to go to their site at all. I'll quite often turn ads on on sites I use ofter, but any site that tries to force me to I just leave and I'd rather not give them the traffic or waste the time.
There are, afterall, plenty of other places that I can get the same information.
The ultimate problem is that an extension can't hide or block content and make scripts on the page think that the content wasn't blocked or hidden; specific approaches can be worked around, but there is no general solution.
Thanks for the suggestion! An AdBlock "stealth mode" isn't in our long-range plans right now. We recommend subscribing to the Anti-Adblock Killer filter list instead. Please see this Knowledge Base article for more information: A website is telling me to disable AdBlock before it will show content