I'm not sure what form the implementation would take, but if all areI like this idea, and would make the tooltip cover the entire box area, not just the slashed-circle "no" symbol.
Only if J's letter badges idea is adopted would I limit the tool-tip to the area of the associated badge (since there might be more than one).
For a list of tags as short as beta's that's likely sufficient. But I
think the addition of a "Also Show Moderator-Only Hashtags"
checkbox (default off) at the top of the list would likely be very
helpful in groups with a larger collection of hashtags.