I'm not sure why we can't get an answer from a BB what they feel about one suggestion or another
The BBs have said they do not want to influence the discussion or people's perception of the importance of certain suggestions or points by commenting individual suggestions. It is easy to imagine a situation where a simple comment by a BB (let's say: "This is interesting" or even "I have read this suggestion") results in several questions targeted at said BB or directs the discussion in a certain way (let's say the BB quoted part of the suggestion text and commented "this is interesting"). The target is to avoid all that, and keep the suggestions purely as suggestions by the community.
whenever a BB reads a message/suggestion, the info will be added automatically.
It is of course possible to implement something like that, perhaps most easily at the thread level. This would perhaps help those users who do not believe the BBs when they say they read all the suggestions. I am not sure what the real benefit is in knowing whether the last time a certain suggestion was read by a BB is today or yesterday. Anyway, no harm in implementing this if it doesn't require too much resources.