This has built in contradictions/near-contradictions, RM, that will cause you headaches.
1. Many doctrines are established by virtue of demonstrating X position as the only viable remaining option. That automatically requires presenting evidence against other beliefs. Immersion Baptism is an example. Any of the millennial doctrines would be the same. Trinitarianism could be included.
2. This precludes discussion of the biography of just about any Christian of any era. Pick any reformation saint who believed the pope to be the anti-christ, and you have a stellar example
3. This violates the requirement many would recognize to combat cultism and occultism whenever it appears.
These concerns are off the top of my head. I'm sure others will appear.
4. It also violates the intent of ecumenism which is an acceptance of differences rather than an effort to force everything into a "bland X" that in its effort to offend no one ends up offending everyone.
On each of the three examples you gave, an article addressing more than one belief and contrasting them would be valid for either an "ecumenic" or "open" tag. The difference would be in the type of posts which are tolerated.
Time will tell.
If, as some seem ‘hell-bent’ to do on the open threads . . .
using EXCESSIVE EGREGIOUS DOUBLE STANDARD PERSONAL ATTACK
stuff to sabotage such threads wholesale . . .
then the new designation will be stillborn.
IF
on the other hand we all try and make the designation work, It will likely be anemic or die because of low attendance.