When I am new to some Stack Exchange site (e.g., this one), I always browse through the available tags to select a few that apply on my question. But, I always doubt if I really have the appropriate once, and then rely on the community to correct them when they're wrong, or when there are some to be added.
A feature like 'suggested tags', would be awesome, but I wonder if it could do more than just suggest the obvious ones, which the author probably already thought of. In your example, I think "X", and probably "A" and "B" can easily be recognized, but "safety" depends on the context, and it thus more difficult to select.
If you are a experienced user, and read the question anyway, will re-tag appropriately right away, to make sure the contents stay organized.
As full automation is not possible, I would say to just let the community organize it.