I'm not sure how useful this would be, since a lot of users would prefer no filter at all. The system also already attempts to automatically organize the posts you see based on your site activity in order to present posts that are more relevant to you before others.
The filter actually hides all posts that don't match your criteria from your personal queue, so you don't even see them. I don't think a lot of users would find that useful or appealing, and they shouldn't be bothered with automated notices about it if they have no intentions of using it. I, personally, would see it as more of a trick to get me to only review things in the tags I provide, due to the fact that the system is asking me to provide them. That's not very user-friendly.
As far as asking for 3-4 tags, the current filter implementation only allows for a maximum of three tags in the first place (and as stated, you will only be shown questions from those tags). There are many users out there that are active in a much wider variety of interests than just three things. The filter is more for finding a specific type of post, and fast.