I havn't seen an idea like this mentioned before.. so here goes..
The last information about tabards I heard from Blizzard was from the Q&A:
ok firstly,Q: When are we getting a tabard tab?
A: We would like to do it, the only reason why we didn't do it yet is because we have click on-use tabards but we kinda want a dropdown or something.
Make them learnable,
Now the reasoning behind them not implementing this according to the q&a is that some tabards are usable.
So the way to fix this is if the tabard has an effect or ability(like a teleport), make it so you 'learn' that spell too, as in, it goes in your spell book. AND add a condition (kinda like a reagent, but it isnt consumed and is a tabard.) to the effect or spell, that tabard has to be active for the effect or ability to work.
This would probably require a separate UI from the equipment pane, probably for both tabards and the effects and/or abilities they have.
If you like my idea.. Feel free to take my idea, steal it, call it your own, and/or bring it up with blizzard, my subscription ran out less than 5 minutes ago so I cant post it.
xD
Happy Holidays.