They don't need the extra adblock detection, they need to validate that a human is watching the ads that do come up. You, as a user with an adblocker, are not YouTube's customer (unless you're paying for Premium, in which case you don't need standard adblock); their advertisers are.
I don't think adblock is such an immediate concern just yet. If they want to cut down on adblock usage, they can just restrict adblock users to a limited amount of videos per day, or limit them to 480p, or pull all kinds of other stunts. Premium exclusive higher bitrate streams seem to be slowly rolling out, but I suspect that's just the first step.
What Google desperately needs is proving to their real customers that they're not scamming them out of advertiser money. An ad not playing isn't costing them much, but an ad playing in a scraper's virtual browser window is a liability.