I don't think a Nerf is especially in order. Then it would effectively hurt at least 1 nation (Vanheim) and limit the use of Blood only to nations with cheap searchers. The only reason that you use scouts is they are the cheapest most availiable form of unit to do the job. It's only a bonus that they are stealthy. If they nerfed the Scouts ability to blood hunt then you'd just use Indep Commanders (50% Increase in Gold and significant resource cost which wouldn't allow you to recruit them in many provinces). If the entirety of all non-blood units blood hunting were nerfed, that would have a significant impact.

When a nation is geared towards blood, then a player is going to use scouts + whatever blood searchers he can grub up (Sages/random cheap blooders) in order to suppliment his blood slave economy. So it only helps blood nations in that regard by allowing them to use their blood mages to research early then go to blood hunting when they need it.

A Nation type that has a bonus (or penalty) to Blood Hunting (People allow it more or less) would be much more in line of what would be appropriate in my mind. However, how hard it would be to implement is as much a factor.

It has been talked about; but I don't know if there has been any real discussion about it.