Dagger Emblem is coming...

It's been possible for a while, I think. Just nobody has done it. However, these daggers aren't the ones that will make it, because being dancers will lower their BST.

Just to demonstrate in vague terms: Saizo as a physical tank, Felicia as a mage tank who will target res if the opponents all have too much def (which is a hard problem to have when all four of your units will be debuffing them like crazy), Jaffar can apply lots of chip damage, S.Kagero or Sothe can be the primary offensive powerhouse or PA Olivia can heal with default weapon and double breath of life.

I've had a dagger emblem team since sothe came out. Jaffar has always done some chip damage, Olivia has been the magic tank, sothe is there to buff and add more defence to legault who is the close counter tank. I haven't been able to pull a saizo yet for a smoke dagger but I made my Summer Linde into a debuffer

To an extent. All their daggers are limited in availability and even then each of the daggers only allows their user to provide a niche roll due to single class effectiveness.