Quoting @Aklapper scoped to just concerns via email (I believe he'll be ok with this):

Asking as I'm opposed to this and would love to archive this tag.

In my understanding, this must be a column on a workboard.

"Needs Discussion" is a temporary status. A temporary status should
never be expressed by a project tag. (We're making this mistake already
with #Patch-For-Review and I don't want to repeat it.)

My initial response:

I think there is a case to be made for using it instead of a column in some cases but if it makes your spidey senses tingle I'll figure something else out.  Feel free to archive it and I'll try to keep my itchy trigger finger in check too.

Note: I added some outline in the description here to flesh things out.

See also T226671: Proposal for global tag: "Needs Discussion"

@chasemp wrote:

it's nice to be able to show only those things in Security-Team that #need discussion.

Security-Team has a workboard column called "Waiting", plus there is a "stalled" task status that a workboard could be filtered on. I admit I don't know what "waiting" means (or for who), but "need discussion" sounds like a subset of it? What's the need for differentiation on different "waiting" reasons?
I guess the scope of both "Needs discussion" and "Waiting" is currently equally vague to me.

To quote @Peachey88 (who remembered the previous iteration, and I did not, thanks a lot!) from T226671#5288465:

a global project as proposed would be non descriptive for this purpose. If a task has multiple projects on it, Where does the needs discussion apply to?

I assume that maybe the majority of all open tasks "need discussion" in some way (apart from tasks which are in a late phase of their task life cycle, or tasks which are very specific bug reports with a clear, single approach to take). So again, the scope is currently unclear to me.
(Plus I can imagine folks who love categorizing for the sake of categorizing to add that tag on gazillions of tasks, but probably I'm overly pessimistic.)

On an abstract "those damn principles" level, I believe that using tags for temporary status transitions is wrong (a better bad example here would be Community-consensus-needed which IMHO should not exist but simply use task status = "stalled" and/or a column on the workboard). I'm reminded of https://discourse.phabricator-community.org/t/workbord-columns-vs-task-statuses-when-to-use-which/511 which mentions both workboard columns and statuses to track progress (or, well, statuses). The proposal here seems to add a third way to that crazy mix.

@chasemp wrote:

I would like to try it essentially

I'm not going to block you. I just think that this is wrong, for the reasons outlined above. :P

thinking about the concerns presented here and keeping the scope of this contained I decided to rename to #secteam-discussion. I think this will contain the proliferation but also let us try out our desired workflow.

Thanks for discussing @Aklapper and the history @Peachey88